Pinging

it sure kinda sorta sounds like that 360 has 11:1 or higher pistons. all the timing changes in the world wont help.

can you find out the history of the rebuild? do you know someone that can do a compression test?

if they are high compression domed pistons, you have 2 choices.
1. run race gas
2. get a carb for E85 (quickfuel sells them) and run E85. if it's available in your area.

if it's not high compression, it's something else. probably not pinging, but some other noise. maybe you have a solid lifter setup and needs adjusting. they make some noise. if it's a hydraulic lifter cam, maybe you have a bad lifter or two. it could be a lot of things.

did the person you got the engine from tell you anything at all about what was inside?