I've been using Tamiya for some time, and have never come across that issue. Perhaps the plastic still had mold release on it? It might also be an issue with the plastic itself, some plastics are known for not holding paint very well, or possibly that the first coat wasn't fully dry yet. One thing I would ask as far as technique goes, are you priming the parts or applying direct to bare plastic? Priming the parts first will give the paint a better surface to grab on to.
They pop up on Ebay from time to time, but tend to go for crazy money. Best bet if you want to find one more reasonable would be to check out the model shows. I've seen them for under $40 (I paid $35 for mine) at the swaps.
For a more simple "back in the day" style exhaust, it wasn't uncommon for the stock manifold to simply be cut between cylinder 3 and 4, ends plated off, and a downpipe welded onto the front half of the manifold to make a split "header" for the Chevrolet 6. Alternatively, if you have it in your stash, the AMT '51 Fleetline sedan kit does have both a decent Nicson dual carb intake and reasonable set of late style Fenton headers.
You're mixing Wheelbase with Overall Length. The Wheelbase is the same for all models '64-'67. The length difference you have noted is Overall Length bumper to bumper, which is different depending on model.
No MRIs for me. Very, very, very, bad for my Pacemaker. I'm not even supposed to go in the same part of the building that the MRI machine is in, as the field is strong enough to damage the circuits in it.
The chassis and suspension would actually be fairly easy to take care of. You'll need to swap the frame with one from the Revell Syclone, and just leave out the transfer case and front drive axle. The balance of the suspension is the same. While GM and Isuzu did not do the same with the US spec trucks (2wds for both kept the standard coil spring suspension), GM did do just that with the 2wd Suburban and the somewhat rare 2wd Tahoe.
Getting back on track, I test fitted a Revell Bel Air sedan chassis (same as the Black Widow) to the AMT old tool body/interior tub. What I have found is that the frame horns and rear bumper mounts will need trimmed down, as the chassis is a bit long, and if the original AMT interior is used, it will definitely need to be cut down. Otherwise, it looks to line up very nicely under the AMT body. Eyeballing it, the wheelbase looks pretty good (I did not have nay suspension components installed), and the rear wheel wells seem to fit fine. http://i281.photobucket.com/albums/kk203/Longbox55/100_3224_zpsjdc0jqps.jpg http://i281.photobucket.com/albums/kk203/Longbox55/100_3225_zpsonhq9iko.jpg http://i281.photobucket.com/albums/kk203/Longbox55/100_3226_zpseka3ynux.jpg http://i281.photobucket.com/albums/kk203/Longbox55/100_3227_zpsbxf3qxyp.jpg http://i281.photobucket.com/albums/kk203/Longbox55/100_3228_zpswara3wxn.jpg
Just checked the dimensions, on the 1:1, there is almost an inch and an eighth difference in width from the front to the back. Here's the dimensions (see page 16) https://www.gmheritagecenter.com/docs/gm-heritage-archive/vehicle-information-kits/Chevrolet/1957-Chevrolet.pdf
Under the bed. The correct stock carrier should be in the kit, or at least it is in the stock version. Since you're going custom, adding the sidemount wouldn't be "wrong", as many of those trucks did get them added when they were customized, especially during the '70s.
I can't really help with a resin source for the fender, but here's the plans for the carrier part of it for the 1:1. http://www.oldchevytrucks.com/images/pdf-1-side mount spare.pdf A note on this, if you're looking to go factory stock, the sidemount was not an option until '53.
That's the nice thing about the Big Block Chevy, unless you're doing a tall deck 366 or 427, plus some of the larger crate engines, the 396-454 are all pretty much the same externally. Personally, as far as the engine itself goes, I find the Revell big blocks from the '67 Chevelle, '69 Camaro Yenko/Balwin-Motion/Convertible, and the '68/69 Corvette to be some of the best overall as far as details go.
The big block really wouldn't be the issue, as there are many kits that have them. The trick would be finding them with the transmission you want. If I'm not mistaken, I'm pretty sure that the AMT '68 El Camino, '70 Monte Carlo, and the '76 Caprice all have the engine/transmission combo you are looking for. If you want to go with a resin transmission, M.A.D. has the TH400 http://www.madmodeling.com/store/ccp0-prodshow/turbo400.html. Kris is a great guy to deal with, and his products are top notch.
I stand corrected, Mark. I thought I remembered reading once that the Datsun used the same chassis. The only one of those MPC flipnose kits I have is the '57, and I have seen the Ford. Same goes for the Revell kits, my experience with them is primarily with the '70s and newer issues.
That is correct about the Revell '57 Nomad and Bel Air hardtop. I have never seen an issue of either kit that didn't include the gasser straight axle. The Revell '53/'54 Sedan and Sedan Delivery (almost always mislabeled on the box as a "panel" ), also have a virtually identical axle, with the wheel mounting being the only difference. You're also correct about the MPC flipnose kit. IIRC, I think the frame in that kit is the same one shared with the '53 Ford pickup flipnose and the Datsun pickup flipnose kits.
Not always. I have pulled agitators out of cans that were metal balls about 3/8" diameter, plus a few that hat metal rods that were about 1/4" around and perhaps 1/2"-3/4' long and rounded at the ends. IIRC, the ones with metal balls were Rustoleum brand, but it's been a long while since I've cut open a spray can.