Re. the 'Excalibur', two further questions from left field:
1. On the plan (see above) I note that the Jetex 50 jet outlet is exactly at the CG. Is that incidental, or is it deliberate? If deliberate, presumably it's related to avoiding climbing or diving under power? But whatever the reason, when adapting to TSP power, should the jet outlet be preserved at the CG, meaning - because the TSP motor is longer than the Jetex- that Former F2 must be modified so that the front of the TSP can extend into the space between F2 and F1?
2. Regarding the point made earlier re. downthrust, I'm contemplating mounting the TSP on a vertical swivel. namely two pieces of thin ply - one glued to the moror mount, the other to the inner fuselage - held together with a single M2.5 nut and bolt, so the motor can be tilted up or down, to optimise trim. Good idea? Or over-training?
Re your questions:
1 The motor was probably placed thus to help minimise the weight needed in the nose, currently we generally place the C.G of an empty motor on the designed CG of the model and add nose weight if needed. However having said that on low powered models the motor can be moved forward somewhat.
2 Keep to the KISS principle, such a mount as you describe adds unnecessary weight and will inevitably get displaced on a hard arrival.