Is the '89 a 3500 or a 2500? A 3500 is a 1-ton, not a 3/4-ton. Not that it matters, but I have a '89 K3500 too, and like the capacity of the bigger truck.
I have opinions, and since you asked, I'll share.
The piece of putting a small block in a '52 that I think causes the most problems is the interference between the steering and the exhaust. If you go with the 235 you can avoid that problem completely.
Or if you go IFS and rack & pinion that will solve the steering problem too.
If you go with the 235 I'd go T-5. I've used a SM420 in a daily driver. Given a choice I'd probably go with the T-5 because it of the better splits between gears and the overdrive.
Staying with stock suspension and sized tires you don't need power steering.
Its easier to start stock or close, and modify later, than to go back stock once you've modified the truck. If in doubt I'd stay as close to original as you can and make more serious modifications only after you've decided stock isn't cutting it for the way you want to use the truck.
I'm a hot rodder at heart, and would probably go V-8 in time but I really like the simplicity of the old 6 and hate to see it abandoned when it is overwise adequate. Try the six before you give it up and swap.
My K3500 is a 454 and I'd go big block in the '52 if it were mine.
