I bought a 73 RT360 that needed new points.  I removed the head to time it. One of the small head studs pulled out it was J-B welded in and it had 2 head gaskets on it. My question is will the head gasket seal with only 3 off the 4 small head studs.

I do not think so, but others will know better.

Personally, I would pull the cylinder, seal off the crankcase with duct tape and install a heli-coil to repair the threads in case.

There not in the case there in the jug and it is to close to the steel sleeve to heli-coil the dril bit would just walk off in to the alumi.

I recommend not using that cylinder. Might get an air leak and cause a high rpm lean condition runaway that could result in a seizure. Previous owner likely had trouble which is why he installed 2 head gaskets.

eBay sometimes has cylinders. I don't recommend going past the second oversize on the 360 as the cylinder wall will be too thin. The cylinder wall on a new 360 is 4mm thick. The 250 is 5mm. And the 250 doesn't generate as much heat as the 360.

Send me a PM if you're interested in a new old stock cylinder with standard, first and second oversize pistons and rings.

Maybe a time-sert would work 

Loctite makes "form a thread" epoxy.  At least they did.  haven't looked for it in a while.  

I've found it works great if you follow instructions.

Also, 1/4" is just slightly bigger than 6mm. Sometimes you can tap 1/4" thread in a stripped 6mm hole and use a 1/4" stud.

I'll try a 1/4 tap tomorrow. If that don't work I'll consider another jug.

Don't panic. What i'd do is try a long hightensile 8mm bolt & you might find unused thread past where the stud finished. Screw it to the bottom then cut the head off for the nut. I've made up 9mm bolts as have a 9 tap & works too. Anyway--i think it'll be ok with three dtuds as you have the 4 big ones holding it all down. Not sure about two head gaskets--second one must be unsupported around the edge & you'd have to line it up square over the top & not bump it fitting the head down. Think i'd just anneal one gasket--red then quench. Grease it & tighten her down. 250 only has the big 4 & is ok. Maybe YZ250A has the extra studs but don't go there. If the alloy is pulled, in my opinion nothing magic will fix it except hellicoiling or similar.

Who said 6mm they're 8mm the 4 studs.