Hi Finster. I might be wrong, but I am pretty sure that your truck would have originally come with 8 lug 17.5" rims. They were standard on the TF 3/4 and 1 ton trucks. The 19.5" size was optional. I don't think that 17" was available from the factory. Not sure exactly what you mean by 'three piece', but the stock rims would not have been split rims.
The good news if you have 17" rims is that you should have more choices for replacement tires than you would if you had the stock 17.5" rims. I think that the only option available nowadays for 17.5's are the STA's. The STA's were available until just a few years ago in both steer and traction tread, but I'm pretty sure that consistent with what you stated about the 17's, the 17.5's are no longer available with the traction tread.
I recently had a '57 GMC one ton panel van that came with the original 17.5" rims and hubcaps. I didn't want to use the STA bias plies, so I replaced the rims with 16x7 eight lugs with the correct offset and installed 235 85R16 tires. If you do the research, you will see that they have almost the exact same circumference as the original 17.5" tires that came with the truck. Like you, I wanted the taller tires to help make up for the gear ratio...and I like the stance. I think they were about 1" wider than the original bias plies.
Sharing this because if you have 17" rims, you might be luckier than if your truck came with the stock 17.5's. You should be able to find a 17" radial light truck tire that will fit the rims and match up very closely in circumference to the original bias plies. The 17" light truck radials will probably cost less, and be a better tire, than the STA bias plies. But you'll need to change front and back.
Matt
