Old Bolens rider info

My son restored this old Bolens rider he bought at an auction (he was frustrated when it was bid up to $13). He restored it for a 4H small engine project, and won the division at the fair! He has some info about it, but would like to know as much about it as he can. He thinks it is from the late 50's (like 58-59). It had a sticker on the back that said "Suburban". Its a fixed deck 26 or 28 in blade. It runs well now (didn't when he purchased, crank case open and full of oats), and he loves to show it off! He (and I) put a lot of time and effort into it (and my money!), but he is so proud of his "trash to treasure" experience, and he uses it to mow often.

Any information (and approximate value?) appreciated!

Andy (and Richie)