A quick update:
Managed to accomplish this between business trips.
Using 1/8" brass rod, I pinned the engine boxes to the fuse. The 1/8" rod is probably overkill, and I probably could have used 2 pins instead of 3.
Shown, is the port side upper engine box. Nearly perfect fit, a little tight, but I'll have a play with the holes and adjust the fit slightly.
The starboard upper didn't go so well. Apparently, 'tolerance stack' caught up with me. That's engineer speak for, ' I didn't measure twice before drilling the holes'. I'll fly my dumb-*** flag for that mistake.
I'll fill the mis-drilled holes with Apoxie Sculpt, and after it hardens, I'll do it correctly.
Once the pins are sorted, I'll remove the engine boxes and its time to build out the wing assemblies.