Keith, I took a look at that video and got this from it.
I have been building models for over fifty years and have built this kit seven times. My guess is the video guy has not been building that long and has only built this one. This would influence his opinion of the kit.
The AMT Grant King chassis is a complex creature. The chassis jig provided in the kit only goes part way towards getting the chassis assembled accurately. It will test the most basic modelling skills. If you don't clean up all mould parting lines and ejector pin marks before assembly, if you don't check the instructions closely and make sure all crossmembers are in the correct place AND the right way around, if you don't use a slow setting glue like Testor's in the orange tube so that you can massage it as it sets up, then you are going to struggle. If the chassis isn't perfectly assembled, you will then struggle to make the body parts fit, on the sprint car or the wedge. When you get everything right, it goes together quite nicely.
But this doesn't mean it cant be assembled and that the kit is rubbish, just that you may need to take more time and care than we have grown used to with modern era kits. I did not have to shorten, lengthen, modify or fabricate any parts for this frame - I just had to give the existing parts my utmost attention.
I completely assembled the entire frame and rollcage and painted it in one piece prior to fitting the body. I glued the side panels to the bellypan and allowed them to dry. I then assembled the nose and let that dry. Finally I glued the nose to the bellypan assembly and put it aside to dry.
I discovered that the deck would not fit over the rollcage as a result of assembling the entire frame already so used a small round file to open up a slot just at the rear corners of the cockpit opening to allow an easier fit. Having also glued those Monogram wing supports to the rollcage did me no favours but I got it assembled without breaking it so all good!
I then put extra superglue over any seams and sanded everything smooth prior to primer and paint. With all body sections painted, I eased the deck unit over the rollcage and down, making sure to keep the sides gently spread so as not to scratch the paint on the side panels. Once in place I glued the deck around the engine area to the side panels as this can never be removed once I glued the wing on - not a kit fault, just my choice of modifications.
Now I squeezed the big block Chevy from an AMT Tobias modified kit into this model and , no, I couldn't fit the valve covers as a result. As I just mentioned, I cant remove the hood so it is of little consequence. I haven't built a Groove Boss with the kit's small block so I don't know if those rocker covers would be a problem as mentioned by the video guy - the sprint car hood certainly fits with no issues at all.
Really my only disappointment with the announcing of the Groove Boss re-issue is that they didn't include the sprintcar body panels provided in previous issues. I think they have greatly decreased their market as a result - after all, the Groove Boss style car is rare to the point that few people have heard of it where as the sprintcar is a classic shape with strong appeal to race car fans and reams of reference material in books and on the Internet. Not one of Round 2's sharpest decisions.
Keith, if you like the Groove Boss style, buy it and expect to spend a few evenings of careful assembly and alignment. You will end up with a nice model!