Do not be concerned about the number of posts you make. That is why we are here!
There were stock 15" wheels available. Some are still around. If you have 16 x 6" rims there should be no problem mounting the radials you mention. However is that 6" measurement an overall width? You have to measure inside to get the minimum width requirement for those radials. My wheels also measure 6" outside width but are only 4" inside and that is where the problem lies for me.
I have the stock rear in my 49 and will drive 50-55 anything above that and I am not happy. A smaller wheel diameter will make your RPMs higher which might negate the 3:55 rear end you want.


1949 Chevy 1/2-Ton
"Sedgewick"
In the Gallery
1989 Caprice