I just received a still-in-bag MAK90 and had some questions. Has anyone tried the ACE stocks on it? Is there anyplace to view a manual online, mine didn't come with one? The action and trigger feel really smooth, do they stay that way or is there a better upgrade? What muzzle brakes do you have, that can be put on by the user, or is it definitely a 'smith job?
I can't wait to shoot it this weekend. Any other suggestions you have for it? Thanks in advance.

Congrats on the MAC-90.
There are lots of things you can do with it, keeping it legal is easy.
First - is it a milled or stamped receiver?
It the end of the barrel smoothed where they took of the threads or is there a nut tack welded on it?
To change it to a 922r compliant pistol grip rifle you need to keep the parts count correct.
A muzzel brake can be pinned on but it does not count.
Most of use buy a USA mage stock kit (3 parts count), change the mag baseplate and follower (2 parts - I have some listed cheap) and then buy a trigger kit and only change the trigger and selector (2 parts) to give us the 6-7 parts needed for compliance.
Russel at RPB had a nice walnut kit for a milled receiver at the last show for $40 - would make a super looking stock if you can do staining and all that. He also has cast trigger kits for a good price but says not to use the hammers - keep your forged hammer.
Also - do not change the gas piston - too many guys forget to keep it wobbly and then the gas tube gets all messed up and fails.
Enjoy.

Here's the manual

Thanks John and dragunov. I just got in the ACE skeleton stock and receiver adapter and put it on. It looks and feels good. The pistol grip and other parts to make it legal are on the way. I appreciate the advice and info.