My doomed 408 build

The WD40 to avoid any 'flash rust' seems fine to me. The immediate assembly was gonna cover everything in oil/lube in this case anyway. A lot bigger things to think about for the OP....IMHO. Last time I checked Smith brothers for pushrods, a set was something like $150-160 shipped ground, for 5/16" ball and cup ones, with a week+ delivery to VA. I made them myself a bit cheaper and a lot faster since I can get the parts from Summit in a day. So plenty of good ways to skin that cat....

Suggestion to the OP: What assembly lube did you use on the lifters and lobes? I strongly prefer the moly based cam/lifter lube. Not too late to get some and put it in at those spots.

Fingers crossed for you. This has been quite an adventure...