beef up? just close the top of the box with any epoxied plate -then I will cut out all the centers of the plates including the engine mount plate.
and make a 1/16" thick balsa cover at the hole in the rear as a "firewall.
I also use 1/2 birch dowels for the engine standoffs - which I epoxy in place and add little triangular gussets - lite and cheap .
We ain't mounting a Buda Diesel- the trick is to triangulate the ply pieces and keep all joints solidly glued -
as for the long Y harnesses - Ifyou can solder - do this: make yer own - using a twisted and soldered joint AND shrink tube insulation, on each joint.
look at how it is done by others ----
Two soldered, insulated connections , lay alongside the single leg of the Y, which goes to the Rx. Do some looking at how it can be best arranged for a neat bundle
When you slip on the shrink sleeve for the final assy - it will all look smooth -
and now you be a soldering expert!
and no more overpriced Y connectors which are the wrong length anyway -