150 psi is gonna require some decent gas to operate without pinging. Do you know how long the present gas has been in the tank and what quality it was to strart with? I think I'd be draining the tank and starting with some fresh 93 octane fuel. My 390 Ford also registers 150 psi and that's what I have to run to keep it from pinging.

"So here it is ... at idle of 900 rpm timingwas set at 6 to 8 degrees after tdc."

If you can't find TDC with the light on #1 wire, how do you know where TDC is on the damper ring??

I suspect that, like many other small block Chevy dampers out there, yours has slipped. My best suggestion is to read this thread.....
http://www.clubhotrod.com/t16722.html