There is one thing to watch out for. The shaft diameter is roughly .489", top to bottom on most of the HEI's. I pulled one out of a 250 that had a lower end of .4666". The shoulder was just up inside the bottom of the gear and below the roll pin and I did not notice it. The bearing was nice and tight so I just dropped it into my engine. It wobbled around like crazy. The oil pump tang was sliding back and forth on the pump slot every half revolution.
I've seen people mount the external coil in weird places. The front bolt on the rear side cover and the rear bolt of the front side cover is suppose to have special bolts. These two bolts should have a stud on their head that the coil sits on and then a nut. That puts the coil just behind the dist.
I had the internal coil HEI, but have switched to the external to give me more clearance for a air compressor that I plan to mount above the dist.
