Ideas on what's causing my click/tick/rattle noise?

Well, I don't know man. SOMETHING happened.

I've often thought it sucked that the slant 6 is so difficult to prime. It has to run basically dry until the pump fills the filter and the engine finally gets oil.

BUT I thought of a way you can actually do it. It's a pain. With the camshaft in the engine and the oil pump in and filter on, you can spin the camshaft with an air ratchet and prime the engine. You don't want to use an impact of course. lol

I just slob lots of engine assembly grease on so the engine doesn't have a chance of being to dry and have at it. I've done the camshaft spin thing once and it does work though.
Rusty, if one is going to spin the complete motor, crank and all to prime it. Why not just wait until the engine is in chassis, remove the sparkplugs and use the starter to spin it.
Then, promptly put the plugs back in and start the motor for real before everything drains back down.