ORIGINAL: Stick Jammer
This project is experimental and likely headed towards a prop engine.
Might be a good candidate for doing away with the tail feathers completely and fly it with elevons. I don't recall anyone trying this but yours seems well suited due to the excess tail weight. It's basically a delta wing and it should work considering how pitch sensitive the airframe is to spoilerons and flaperons. In it's present state it sounds like you're gonna need more power than a glow engine can produce as prop size is limited.
Yes, power will be a problem.
I have an older ST 90 (removable front housing and hope it will run backwards) and a 12 x 8 three blade prop laying on the bench for consideration. It will probably fly with the .90 but minimum flying speed is likely to be in the mid 30's.
Your delta suggestion is interesting. The tail section weights 1 pound 7 oz or so with servos. Maybe the delta suggestion can be tested with the skinny Bob Cat first since I have zero delta experience.
What is really needed is more wing area. All recent military aircraft have supplemental wing area in front of the main delta wing. The cardboard mockup below of additional wing area might be easy to try. It also might not work. This type of conversation often results in serious breakage.
The heavy airplane is simply too pretty to retire.