After I bought two M70's (B1 stock and AB2 underfolder) I realized that they aren't actually Yugo AK's. Wikipedia tells me that they are Yugo versions of the RPK. I did not know that. Actually, I didn't know what an RPK was either, but Wikipedia helped me out there, too. It's basically a beefed up AKM. (I like Wikipedia)  

I've noticed that the M70's handguard/gas tube/receiver cover/barrel trunion are different than those on an AK. Wiki says the the barrel is threaded instead of pinned. And the receiver is noticeably thicker and stronger.  The receiver cover and gas tubes are longer.

So......other than the magazines, what parts are interchangable between the M70 and AK? Are the bolt and bolt carriers different? Will the parts in a standard AK "field repair kit" work in the M70, or do I need to buy some kind of "M70 field repair kit?"

well you are partly right.

they ARE yugo ak's, just yugoslavia decided to use RPK type trunions and 1.6mm recievers so that the rifle wouldnt take such a beating from launching grenades. the handguard and gas tube are slightly longer than other countries.

p.s. dont trust wikipedia

your m70's have a pinned barrel, only m64's had a threaded barrel.

and the ak repair kit should interchange,  someone will chime in if i wrong about the repair kit

Id like to know if the Gas Piston will interchange with the new US made ones..

should be GTG on gas piston change. The only one that is odd is the yugo krinks

Can't figure out how to put column spacing in a post, so you will have to copy down this info and add your own spacing to make it readable.

Compatibility between Mitchell-import Yugo AK M90, M70. and Norinco and some Chinese/Bulgarian AK parts - from actual experience.

                             Compatible?      Comments
Bolt                               Y                Norinco and Bulgarian work ok, tested
Bolt carrier                    Y                 "       "          "    "  same LOA as bulgarian and chinese, same dia gas piston
Gas piston                    Y
Recoil spring                 Y                 OK, but Bulgarian has a small tab on the rear button.  Could be ground off easily.
Top cover                     N                 Yugo top cover is about 3/8" shorter
Trigger                          Y                 Double sear hooks
Sear                             Y
Hammer                        Y
Trigger pins                  Y                  But are slightly short
Safety/Selector             N                 Yugo selector is longer than Norinco/Bulgarian with different stops
Gas tube                       N                  Yugo gas tube about 1/2" longer
Top handguard             N                  Yugo handguards longer than Norinco
Bottom handguard        N                   Yugo handguards longer than Norinco
Buttstock                      N                    Different butt socket than other AK's
Pistol grip                      Y
Front sight                    Y                    Appears to be the same, but not tested
Front sight slide           Y                    Standard dia is .394", Yugo looks to be the same.
Rear sight                    N                    Yugo sight is slightly shorter.  Should interchange, but ranges will be off