Wolfclan. Just because you had an FFL doesn't make you the authority. Pistol grips are perfectly legal. As are Folding stocks.
All you gotta do is be within the OAL and barrel length of the gun.
Here is the actual text:
16. Do rifles or shotguns with collapsible/folding stocks have to be registered in Michigan?
MCL 750.222 Yes, provided the rifle or shotgun is 30 inches or less in overall length with the stock collapsed/folded but at least 26 inches and the barrel length is at least 16 inches and 18 inches respectively. Attorney General’s opinion #6280: if the firearm is less than 26 inches in overall length or the barrel is less than 16 or 18 inches respectively, the firearm is considered a short-barreled rifle or shotgun and is illegal to possess. MCL 750.224d There is an exception for short-barreled shotguns and short-barreled rifles which the Federal Bureau of Alcohol, Tobacco and Firearms has found to be a curio, relic, antique, museum piece, or collector’s item not likely to be used as a weapon.
this is why they sell them at gun shows and shops. cuz it's legal.