You would more than likely be able to get a good enough look at the crank just by taking a cylinder off. If it says hotrods, Vesrah,etc on the rod you atleast know it has been rebuilt and you can also see the webs, not 100% accurate but your just curious anyway. If you wonder if it's a 4 mill just pop the head off, if the piston sticks out the top of the jug 2mm thats what you have, unless there's a spacer plate under the cylinders.
It's easy to tell if a stock head has been rechambered for a stroker crank but to tell if it has just been milled would probably require cc'ing the domes, or if there is visible cutter marks on the mating surface.
As far as a replacement clutch goes, I recommend the one Jeff at F.A.S.T sells, it holds alot of power.
If you have a good running motor I wouldnt be tearing it down just to see what you have, run it until it needs rebuilt then check it out.