Completed 2 test drives..... after shortening the cable linkage it finally got 2-3 psi boost. That's almost what was expected for using a rain cap as a valve..... no attempt was made to improve the seal at the mating surfaces. Plus the boost pressure has some leverage to force it open.
But nothing terrible happened on the tests, so now I'll try to come up with a non-leaky valve
Ha, just remembered I forgot to reflash the PCM for the stock MAF