On my World aluminum Hemi raised cam block I had similar grinding to do, rounding out the top portion of the block to make it fit took the most time. Used a 4 1/2" grinder with a course wheel to rough it out then a flap wheel to smooth it out. Can not tell any work was done. I was quoted $75. to have it fitted at the machine shop, took about 15 minutes for me to do it

it's ok to butt heads, just don't do it with a butthead