The Tapco mags run just fine, especially if you do a couple mods to them and/or to the rifle. The bolt needs to be ground in a couple places to accept the mags and to allow 'full' loaading'. The mags need a couple slight mods too, one to 'clear' the front of the mgs into the well; the second is to allow loading with a stripper clip. Here's a quick link to a thread on SKSBOARDS .COM that briefly describes these. You can find LOADS of SKS info there, for all flavours of SKSs.
http s://www.sksboards.com/smf/index.php?topic=151002.0;topicseen
As for other mods, one of the best is painting the rear sight White and the front post Red - it makes acquiring target much easier with the irons. There are mods to the trigger assy if you're mechanically inclined, too. I have a '51 Tula that I've got the trigger down to ca 3-4# and can hit under 2" at 50 yds. with the irons. That's OK for a 70+ year old surplus rifle that's been used 'harshly' b4 I got it.