I was presented with a problem with my first bellhousing adaptor on the back of my engine block. The early blocks like I have used 11/16 bolts for the bellhousing attachments. I'm using an 1/8th inch trans adaptor plate as part of my set of adaptors. I wanted to attach that first plate with two of the early bolt holes not used on the late pattern. Using 11/16 flathead (countersunk) bolts it left the heads sticking too far out from the plate, intefering with the second plate. So I had to find a way to grind down the tops of the flat head bolts evenly. I don't have a sanding table or mill etc. Only good ol' imagination. I do have a bench grinder so I took the bolt, placed the threaded shank into a 1/2 inch deep socket so it was loosely setting in the socket. By hold the bolt head flat against the grinding wheel (the face not the side) bu toffset so it only contacted one half of the bolt head, the grnding wheel not only ground the head down but by being offset and loose in the socket, the bolt spun evenly grinding the bolt head. Plus, the loose bolt in the socket did not transfer the heat from the grinding to the hand held socket. Worked great.