Wheel sizing and gearing

[Aussie Boy]

1965 C10 fleetside, 230 engine, SM420 Muncie and a 12 bolt rear end. I know with retaining the gearbox I'm battling for top end speeds and low revs but the wife wants the truck left pretty close to standard as it belonged to her father.

With that being said we're lowering the front 2 1/2" with spindles and the rear 3" with springs. Would 17 x 8 wheels covered in 235/75R17 clear the guards and not rub on suspension or steering?

Those wheels will put me around 30" high which will help with engine revs at speed, but what ratio in the rear end would help out? I've used calculators online which gives me an idea (3.73), but I figured asking the guys that have been there and done it would help out also.

Cheers fellas