As previously stated. The only gain you will see is improved load carrying capacity of the 19.5 tires. Your chassis limitations will stay the same. Your 235/85R16 tires will actually ride better than 225/70R19.5 tires, due to the taller side walls of the 16" tires. They are both 32" (+/- 0.20") in diameter and will not affect your speedometer. The wheels you need are 3/4 ton, 10 hole, Chevy PU wheels, with the center hole opened up to match your hubs.
Rickson Truck Wheels has those wheels.
I own a 1995 F53 Bounder that drives good and rides good for an older gas chassis. Make sure you have 5/32" toe in, make sure all steering components are in good shape, keep the king pins greased well, unload the front axle when greasing the king pins, or they will bind and not drive well. Add a front pan hard bar and your F53 chassis should work well for you.
Richard
TDY: Grande Prairie, AB. Next stop, Fairbanks, AK
95 Bounder 32H F53 460
2013 CRV Toad
2 Segways in Toad
First brake job
1941 Hudson