Thanks for the replies. Great to hear there are a couple guys close enough to check out some other 520's when (not if) I get stuck!
I pressure tested the boiler at 60 psi and have zero leaks. Hopefully the parts I need to make a test fire will arrive tomorrow. If that is the case and we can build a fire in the pot, we can stack the two parts together!
Looking forward to some plumbing and wiring. As recommended, I plan to plumb the return back into both lower ports. On the right side, there is a 3" x 1/1/4" bushing. On the left side, there is what appears to be a factory installed 3" x 3/4" bushing...or at least installed a LONG time ago. I didnt try very hard to take it out, (only a 24" pipe wrench and no heat) but it's most definitely tight. Should I do whatever it takes to replace that bushing with an 1 1/4" NPT or would one 1 1/4" joined with one 3/4" return suffice?
Havent forgot about posting some pics. will get to that...maybe during our test burn.