A little bit of knock under those circumstances is acceptable, as long as it is not excessive. But the fact you want to eliminate it is fine, you just retard the timing from the original setting.
The Chev engines for 1972 (according to the refs I have) are:
4 degrees BTDC for the 6-250 manuall or auto, 307 w/manual, and 350 (4bbl)w/manual
6 degrees BTDC for 350 (2bbl) auto and manual,
8degrees BTDC for 350 (4bbl) w/ auto, 402(396 labelled at times) with either transmission, and the same for the 454 with either transmission.
I would also verify that the pulley has not "walked" on the damper to throw off base timing references.
If currently you are running 4 degrees BTDC with a knock under the extreme pull of a hill, it can be caused by the oxygenate in your pump gas, or carbon buildup in the combustion chamber, or even a hotspot if the crossover is plugged.
A shortcut method is to retard 2 degrees and test for knock, and repeat until it goes away, but
you may end up firing after top dead center, and performance overall will be poorer.
Or you could start adding an octane booster that does not contain ethanol. <img border="0" alt="[twix]" title="" src="graemlins/twix.gif" />
:confused:
