Minimum wire harness for engine operation?

[CrankyOldMan]

tl;dr - I'm hoping that someone here has experience with setting up a 1NZ in a minimal install state, or at least getting one to fire up when removed from the vehicle.

I'm planning to do a 1NZ-FE swap in my MK1 MR2 in the near future, and I'm gathering intel on the electronics side. It's my first engine swap, so there's a lot of undiscovered country here for me.

I've got the EWD for the 1st gen Scions and I'm comparing it to the Echo wire harnesses that I've seen on ebay. The ECU has 4 plugs: 2 go into the engine bay, 2 go into the interior. It looks like the main engine wire harness will cover all of the basic connections (battery, ground, injectors, coils, etc.) and since I won't be using any of the interior stuff (A/C, radio, window motors) I don't see a need for the two interior connections. Of course, that all depends on what wires are actually in those other two connectors. I'm laying out as much of the EWD as I can in a separate schematic to verify all the connections, but it's a huge spaghetti mess, complicated by the 2006.5 change and the AT vs MT differences.

The plan is to use the existing instrument cluster since all of the indicators are standalone gauges, but add the OBD-II port for diagnostics and possibly monitoring other systems. There's a guy that's already done a 1NZ-FXE swap into a MK1--and can do the wire harness for $400--but I would like to do the work myself and save the cash. There's also the option of building a MegaSquirt ECU and doing away with the OEM ECU altogether, potentially in concert with forced induction. I've got a salvaged Blitz S/C kit and a brand new Ogura TX-07 compressor that can be pieced together to that end.

I've also go access to pin crimp and removal tools for many popular types of automotive connectors at work (Sumitomo being one of the biggest pains in the ass) so I could in theory do it without spliced/soldered connections.

So what say you, YW? Do we have the collective knowledge and experience to pull this off?

EDIT: added link to pinout

2000 Echo ECU pinout