Anybody seen a universal joint socket set with hex head bits for Allen head screws? Gearwrench sells one, only one, with a 6mm hex head. https://www.amazon.com/GEARWRENCH-81083-Universal-Metric-Socket/dp/B00SQ4DVRG I've got one 1/4" socket head (Allen head) valve cover bolt buried next to the A/C cover (right side rear bolt) on my '75 Ranchero 460. The head is a 3/16" hex. I got the danged thing out. Now to get it back and tight. The 3/16" hex socket with an add on universal joint socket is just a bit too long to get fully seated in the Allen head screw.
Well geezery. I could just cut off a spare 3/16" Allen wrench and fit the hex end into a standard 3/16" universal socket which I already have. Like this: Worked too!
There ya go! Yeah, that corner's a bugger on a 460, due to the low amount of clearance to the evaporator box. I did a 460 cylinder head in a full size wagon, and that one bolt has to stay in the head, both coming off and going on, as you will not get the head off or on.