Alex

At that weight and size a 54 size turbine will provied more than enough power. you may even be able to de-rate it a bit and save on fuel consumption....or climb very fast.
If you are worried about heat on the fin make up a simple heat shield. This can be done from lithoplate folded around the front of the fin. set it forward of the fin by 15 to 20mm and attach it to the sides on the fin with 3mm spacers to allow an air gap. I was concerned that fitting such a sheild would have an adverse affect on handling but it made no difference. You can see the heat shield in the posted pictures.

Regards

John