So I have a 2001 GSR with about 135k on it. Three of the cylinders have low compression. I haven't taken the head off yet but I feel like the piston rings are what's bad. Would it be worth it to swap in another B series engine to sell the car? Or should I try to get the B18c1 running again? Thanks.

 

Leakdown test to confirm the rings are bad, HG is blown, valves are sealing, etc... I'd work with the block you have for now.
I wouldn't buy an engine to sell it, too much risk and effort for little potential gain, IMO