Huck Hold Down Springs
That's got my curious , I've not had any Huck drums off in many a year , and in looking at the various pictures and trying to recall , I wonder of maybe the fact that the shoes are pinned in place by those wretched link things at the bottom , means the hold down spring wasn't always used.....
I'd not be drilling any holes nor making other changes just yet ~ don't you have a copy of the FSM for your truck ? they're cheap @ $29.95 and usually pay for themslves the very first time lookng at them solves a question like this...