OK, well first off, don’t spend a lot of money on this project! That piston isn’t scored that badly, even though it is on the exhaust side, these engines are pretty tolerant and I’m sure it will idle fine that way. Do check the ring grooves though, looks like one of the grooves might be galled slightly. The scoring is probably from a bit of overheating, or perhaps not quite enough oil in the gas. Look at the rod bushings/crank journals carefully, these areas are the weak link for these bushing motors. You should try to measure the cylinders and piston skirts just to be sure nothing is distorted also.
Like Dan says, the taper pins get driven out the other way, from cylinders toward intake manifold, they are reinstalled in the opposite direction. There is a good chance that the mating surfaces will get messed up due to driving these pins the wrong way, so please check the crankcase halves for flatness once the pins out properly/safely removed. The engine definitely won’t run right if the mating surfaces are messed up/not flat. Do not try to "resurface" the mating surfaces either, this will just jam the crank in the journal bushings.
Looks like you have identified most of the drain passages. Don’t forget to check the upper seal/slinger vacuum port and lower to upper oil recirc nipples/passages.
Again, don’t spend a lot of money on this project, just gaskets and rings. There are plenty of used donor parts out there for anything else you might need.
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