[cebra]

I would just get grade 5 or 8 washers and go with that. I am not familiar with the 4L70E but it should be pretty straightforward.

A few things I would do while the motor is out: check brake lines on crossmember, clean and paint everything you can, check/replace seals on transfer case, check replace fuel lines from tank to fuel pump. That is about all I can think of right now that would be much simpler with the motor/trans out.

When putting new motor in, hook up oil pressure line as motor is going in as it is tough to do once the motor is sat in place, watch the distributor clearance vs firewall if installing that first (I do, most don't).

Really there isn't a lot that would require "pulling the motor back out" maybe if you put your mounts in the wrong location/wrong mounts, if oil pan doesn't clear crossmember, something along those lines but you would figure those out pretty quick. No need to worry about rear main or torque converter on a new package. Everything else is pretty easy to get to with the motor in or out. Trans lines are kind of a pain but you will need to do that after the trans/radiator is in anyways.