mix up 50~50 Acetone and Dexron III transmission fluid and bathe the stuck stud with it day and night. After a few days use a hammer to see if you can induce some movement and use more of your penetrating oil mixture to induce more movement.
When you eventually get the stud out, use a stainless steel (ground) replacement and coat it with your favorite copper based anti-seize compound.
As far as spacers go it is a bit of a raffle. Your bike may or may not have had "solid" mounts, or it may have once had cone-couplers. The size of spacers is really down to what your bike needs as the frame hoops may have been closed up, or spread, by past owners doing stuff.
P.S. If when you have it back together your bike is one of the rare ones that gives you "tingles" particular rev ranges - vary the tension on the engine studs to move the vibration to a rev range that doesn't annoy you.
