I can see chopping up a mag and shortening it, possible. Probably have to shorten the spring too.

The upgrades I've found through asking on here and Googling the crap outta the 64 are:

Longer charging handle, extended mag release, and Picatinny slip-on-dovetail rail from DIP www.diproductsinc.com

and a Trigger Spring Set from www.mcarbo.com

Personally, I have the longer charging handle which helped tremendously, the P-rail which took some persuading to get on the dovetail, and put a bipod on it too. But, if you have newer 64, it should be drilled/tapped for a rail/rings. Mine's an older one and has the dovetail.
To tighten your trigger up some, squeeze together the frame the trigger sits in at the back. When I took mine apart, it was gapped and the trigger has side-to-side movement, went away after a pair of pliers was GENTLY used. I might get frothy and buy the spring kit one day...