Did you forget to put the oil in, Dave? Just kidding. Was this engine a recent runner with no issues aside from a leaking rear main? I don't see how the parts you replaced could have any bearing on your start up oil pressure or prevent the lifters from pumping up. Do you have a mechanical pressure gauge hooked up by chance? You can always pull a valve cover to see if it looks like you're getting any oil to the top end. You could even run it briefly with a cover off, but it makes a hell of a mess if oil is getting up there. I'm working on forest fire suppression repair every day of the week, or I'd buzz up there to the big burg, let you buy me lunch and have a look see at the thing with you.