I don't have a 359, I have a 327, which has an 8.0 compression ratio. I get about 120 psi compression when running a compression test after having rebuilt my engine, though I didn't bore the cylinders, just new pistons and rings. I only tested the compression after having got the new engine started. Folks say you don't want to run the engine purely at idle for break-in, you want to rev it up and down the rev range some.
I have seen this rule of thumb used - multiply the pressure at your elevation (here I use sea level) by the compression ratio to get an approximate number:
14.7 psi*8 = 120
The 359 has an 8.1:1 compression ratio, IIRC, so you should get about 130 psi.
Compression and Leakdown test 75 psi seems pretty low to me, but the rings do seat with break-in, and I would put a little bit of oil in the cylinders if you are doing this test before running the engine at all.
Other folks should weigh in with more experience than myself, having only done this once.
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