Tired of DIY!

I think your comments give you a good plan of attack...
First, I'd get rid of that old gas if I could to eliminate it as a variable. Gas can go bad within a couple of months if untreated, although I'd suspect that's not your problem.
Second, get some of that UV testing dye to really see where the oil leak is coming from. You don't want to pull the engine again if you don't have to.
Third, did you check the valvetrain geometry/pushrod length? If you have and it's good, play with lifter preload. I've had valvetrains that were loud at 3/4 turn quiet down at 1/4 turn.
Fourth, make sure your vacuum ports on the carb are plugged (regarding the carb whistle). I've had carbs whistle with certain spacer designs, as well.

Take a breather, regroup, and go at it again...some problems seem to solve themselves after a good night's sleep. I'm sure others will have other suggestions, too.