Thanks everyone!
The first challenge was converting it to a 4-engine layout. It's a quirk of the kit that it's sold as a Cargotrans C-160, a real plane which somewhat resembles a C-130 with 2 engines instead of 4, but it's clear that the foam pieces are those of a C-130, the biggest giveaway being the dolphin nose.
The included nacelles were too large to mount 4 of, so I designed and 3D printed my own in resin, modeling them to fit the curve of the wing and dialing it in through trial and error.
I designed them with 1mm thick walls, printed in Anycubic's ABS-Like resin, each one weighing ~10g counting both peices. All 4 nacelles or all 4 front covers fit on the print bed of my Photon Zero. Final versions were printed in grey, I just happened to have white in the vat and knew I needed to prototype a few anyway.
I added tabs to the final versions which slot into the wings and are glued in for a very snug fit:
The entire power system is borrowed from quadcopter tech - A 4-in-1 ESC, the props were a quadcopter set, and the motors are used pulls from some unknown model of drone. (makes me wonder... post drone show motors? maybe they replace entire fleets at a time)
I bought 5 motors to have a backup and sure enough 1 of them overheated during testing while the others ran fine, pulling 2.3A on 2s, producing ~100g of thrust, and ~200g of thrust on 3S, drawing 3.7A - pretty close to prop calc's numbers, current draw actually lower than expected. Those were the individual motor tests, I'll do a whole-system power and thrust test soon.
This means it should run on anything from a 2s 800mah to a 3s 2200mah, which I will test shortly.
Mounting 4-blade props was one of the goals I had in mind selecting motors. There's not many options in that size range, but I found some
5x4x4's sold as a quadcopter set that seemed promising.
I found some
1200kv motors on AliExpress that only weighed 21g, this was a breakthrough - I really like small motors with low kv's, they can turn surprisingly big propellers for more realistic proportions.
Since wiring up 4 ESC's would have been a nightmare of wires in an already cramped space, I went with a 4-in-1 ESC intended for a quadcopter, but since that lacks a
BEC, I soldered on a little 5V/3A converter directly to the voltage inputs to turn it into a "fixed-wing" style ESC.
I tied together all 4 throttle lines, and together with the
BEC, I had a standard servo lead for my receiver.
To change settings on the 4-in-1 ESC to more closely match a fixed wing's behavior, I had to buy a little flight controller to use "pass-through" because I couldn't get any of the serial protocols to connect directly to the ESC or via intermediate programmer. I raised the demag compensation and set a delay on the throttle to avoid hard stops when I throttled down, which I noticed was an issue with the stock configuration.
I 3D printed little platforms with more tabs on the bottom that glued into slots in the wing, one with screw posts for the ESC, one with zip-tie holes for the receiver, not yet attached in this pic:
There's 12 wires tucked into each "trench" in the wings - 2x sets of motor leads and 2x servo cables for the flaps and ailerons.
to be con't...
My brain just does'nt want to figure stuff out anymore, I'm turning into a plug and play guy. 
