I did check the Remington website. The Sportsman 58 was made from 1958-1963, but nowhere on the website did they have a PDF file for a manual or any disassembly info. I e-mailed them for anything they could tell me, but I figure that'll take a few days. Thought I'd check here, also. This one is mint, no blueing wear or dings on the wood. ,It has a 26" Modified bbl w/o a rib. Thought I'd hunt grouse with it, on days I didn't feel like cleaning my primary scattergun, a Pedersoli SxS 12ga muzzleloader.
The Pedersoli is a great upland gun. Chrome-lined bores and choke tubes aren't in keeping with the period, but it's a lot easier to shoot and maintain with them. It has hooked breeches and cleans up pretty fast. It points and balances like a good bird gun should, but recoil is stout with heavy loads, due to light (6.5#) weight.
I got the 58 apart and cleaned up. It had a small rust spot where the bbl extension goes into the reciever, and that make taking the bbl off harder than it should have been. Bore and exyerior are mint and the gas system looked like it had never been fired. I'll try it out on grouse soon.