To summarise the above, I would:
Check your timing marks with a piston stop. The way you do this follows:
You need a stop that you can adjust, and you are NOT trying to stop the piston "at TDC" but rather DOWN into the bore some amount, not critical. The reason for this is that as the piston aproaches, goes "over" and down again, the piston slows down, and becomes difficult to resolve near the top
So make sure the no1 piston is "down a ways" install the device, and unhook the battery. Wrench the engine until it stops, and you may have to adjust the length the first time around. When the engine stops against the device, make a temporary mark exactly under TDC of the timing tab, onto the balancer
Now turn the engine left (CCW) and do the same thing.
You will have two marks some distance apart, and true TDC will be halfway in between----if the original is correct, that is where it will be
Determining if the cam drive has "slipped." "Depends." If there is some wear on the drive, and ESPECIALLY if it is one of those @*@($&*@#&$*)@#$!%#^_&U#$# plastic sprockets, be suspicious
You can get some idea of chain wear/ play by watching the rotor, and wrenching the crank back/ forth against the "slop" which you can feel with practice. If the crank moves 10* before the rotor moves, it's too much
Determining if the cam is in time can be a little more difficult. If you have specs for the cam, you can see where one of the timing events happen.
MSD---I'm not intimitely familiar with MSD stuff, I don't use it. But SOME of them have advance/ delay stuff built into the box, and if your's does, this might be an issue --changing the timing when unwanted
If you don't have your balancer degreed, either do so, or buy the proper timing tape. IF you are using a "dial up" timing light, SUSPECT it might be inaccurate and round up a conventional light to double check
