Not up on the Mk2 and 3 differences, but before you start planning you new arm and what mods you will do, fit a really good cart, and listen to it stock. Maybe a damper trough will be a good mod, also modding it to take any rcas is a good idea, but why mess with a perfectly good plinth?
My Sl1210 with a stanton 881 with a Jico stylus or my Decca super gold sounds amazing. Mine is stock apart from an arm rewire and rca leads. When I bought mine I was going to change the arm , psu ect but when I heard it I left it mainly stock as in my opinion it is excellent as it is. The Technics really needs the right cart to make it shine this is were you should start.