Welcome Sparky - Always great to hear about the "fathers son" projects. My son has a 71 C10 pickup and we've had a lot of fun working on it. A bit simpler than your 86 however!

As to the instruments - are they working now? The senders from a later model 350 should transfer pretty straight forward. Oil pressure sender and water temperature are perhaps in different "holes" in the engine but you should be able to relocate them (i.e., oil pressure is in the rear - near the distributor and water temp in one of the heads) to the crate motor and have them function. I'm assuming that you're going to use the same alternator so that should be no problem.

Others will chime in I'm sure.

Good luck and enjoy this time with your son!
Glenn