Since no body else mentioned it, the tabs on the front of the frame rails were for a tow bar that was in the old AMT 32 roadster. The tow bar just hooked over the two tabs. I also like how well you brought this back to life. I think my first car model was that AMT roadster.
I like everything about it with one exception. Color is great and goes well with the interior. Engine looks good. The only thing that bothers me, and it could be just me, the radiator shell seems to be too high. It doesn't seem to flow into line with the body. Don
I had one as well. I put 160,000 miles and 2 engines on it before a got rid of it. 2.8 litre V6 and 4 speed. It handled really well and could sure surprise a lot hot cars of the time. I don't know how fast it would go since it had one of those 85mph speedometers but you could easily bounce the needle of the post. I don't know if you are going for stock, but if so, the engines were red including the intake and valve covers. Neat finned aluminum valve covers.
Quick internet search results: Chrysler 300B - 353 ci, 218.8 in. overall length and 126 in. wheel base Desoto Adventurer - 341 ci, 220.9 in. overall length and 126 in. wheel base Not a lot of difference.