[25stevem]

All the 67 400 blocks and the early 67 428 blocks all had the top of the Bore chamfered for earlier 17 degree inclination angle of those 326,389 and 421 heads heads.

If you want the best Intake breathing when running any head with a 2.11" valve then the chamfer should be added to the top of the Bore as was done for the latter 14 degree heads.
Doing such depends on the chamber your working with and the compression you want/ need for the Cam your running.

Adding the needed chamfer will add near 4 CCs to your calculations for compression.

On most common Pontiac Bore sizes 4 CCs will change your ratio by a 1/4 of a compression point, so if that's a problem you can easily mill the heads or deck the block to retrieve those 4 CCs .

If your getting custom Pistons made then increasing the compression height by .018" will make up for the 4 CCs you put in from getting the valve Bore notch in the right place

Note that boring the block .045" over will remove about one half of that unneeded valve notch that was held over from the 17 degree heads.