Well, I think it's about time I got this party started, having decided that "to make things easy", I'll go the route of a Turnigy G46 motor to replace the recommended .40 or .46 IC motor. Obviously, it's easier to modify as I build, so the first consideration is a hatch to get at the battery as I really am lazy and don't want to have to remove the wing each time. I want to have 2 batteries; one to fly while one is on the charge, so not going to go the route of "charge in place". Thing is, the space between formers isn't sufficient to ease a battery in. I think that the only option is to cut the top off one former (the one on the right between the jig brackets) to make a "U" former and strengthen the hatch opening with 3mm ply. To that end, I've cut the ply reinforcement first and made two "brackets" to form the front and rear of the hatch out of two layers of 1.6mm balsa laminated together at 90°. They won't be loadbearing, so I think they should be strong enough.
I haven't cut any formers yet, just in case anyone advises against the plan! I'll bow to superior knowledge and craftsmanship.
I've filled in the predrilled holes in the firewall as I intend to use a Great Planes adjustable motor mount to hold the G46 and the fitment is different.