Aaron, the AMT '78 Ford kit has a F-150 4wd set up in it so it is accurate for the Moebius kit as long as you are depicting a 1/2 ton 4wd F150 truck. The F250 and F350 trucks had leaf spring set ups while the F150 had coil springs and radius arms, like the Bronco.
Check with some of the guys who sell collections- Jim in Ohio, Fred Sterns, Dean's Hobby Shop- they might have one or might have one coming in soon. If you have any shows coming up in your area, you might find one there.
That is a 1/10th scale light bar that would probably look cartoonish on the Meng F350. I don't have mine in front of me, but if I had to guess it would be rather large compared to the rest of the model. Your best bet would be to scratchbuild one, shouldn't be that hard/
A couple of things about The Modelhaus: 1. As mentioned, they will be retiring and since the announcement, they have been swamped with orders. 2. Earlier this year they lost their youngest son suddenly and closed for a couple of weeks while they dealt with the unexpected tragedy. 3. They have some stuff in stock, but many times cast parts as they receive orders, so no matter how small or big your order is, it might not be ready for awhile. 4. They have a system where orders are shipped in the order they were received, so even if your parts are in stock, they clear the oldest orders first before getting the new orders out. 5. Don and Carol have a great business and their quality and service is something all companies should imitate. I have been compiling a list of parts and kits I want from them and will be placing my order soon, knowing that it will take awhile to get. Have patience, you will love the product.