First I wouldn't bother with the wideband, yes they are helpful but Not needed in your case.
You said you have an 83 l28et swap, Then you mention your dry compression numbers which were good numbers for a turbo engine( I believe stock compression is 142psi). But then you showed a compression test with oil in your cylinders which jumped up to the compression of an N/A engine. Then you said you preformed a leak down test which showed 45%-60% leakage! Thats crazy high. Anything over 15% leakage generally suggests a problem that needs some attention.
At this point I am convinced you have an N/A engine with excessive blowby(did you verify the leakage wasnt also coming out of the intake, exhaust, or head gasket?) If you have been driving it in this bad tune for some time now it makes sense why things have gotten progressivly worse for you.
Your engine clearly needs some attention. I would fix your engine and go back to the stock turbo EFI. The 300zx set-up will just complicate things.