MK2 completely different stock, reg in 12FP or longer fast flow in FAC (FF is same length as a reg, not like the shorter bottle adapter on the MK1). You can also have regged FAC, but needs a bit of fettling from someone like KevG.
For FAC, the more efficient porting of the MK2 should give you a few more shots, but if you find a good deal on a MK1, I'd be happy. I had both on 12 FP and FAC, and they were all good. Just choose the one where you can most easily confirm the accuracy, preferably with either 16 or 18 grain pellets, as some only work well with Bisley Mag or similar 20+ grainers. At 30FP, you are pretty sweet in terms of power vs air use & noise, but that's a bit low for a 21 grain pellet in terms of trajectory.
Also test the triggers - some are fine, some are a bit crap. MK2 triggers generally better.
Don't rule out MFR either.
Always looking for any cheap, interesting, knackered "project" guns. Thanks, JB.