Hey Gonnut congratulations on " stepping up" an expression thats sure to induce a lot of ire with some of the electric enthusiasts
First things first it will serve you well. May i suggest since you are already operating a 2.4 system, yes yes do get a receiver and fly your ship with 2.4. The advantages are to plentiful to list and outside the scope of this thread.
The existing servos will be fine There may be some plug compatibility problems which are easy to fix unless they are old style Airtronics servos with black servo plugs.
I would definately not recommend using a 4.8 flight pack especially since you will be flying with a 2.4 system. I never use 4.8 packs with 2.4 , the advantages are many. For that airplane may I suggest a 6.0 (five cell) volt Nimh pack of 2000 mah. This will provide you many flight during the day and What I use on almost all my glow airplanes. The cell size of that pack is AA and its only slightly bigger than the old 4.8 Nicd of far less capacity. This pack is ideal in your trainer.
Another likely problem is the fuel system tanks tens years and older tend to have many problems that you can end up pulling your hair out over. its the conventional bung plug type that suffer the most and instead of fooling around trying to replace dried out and hardened bung plugs as well as leaky tank internal fuel line, I do myself on this stuff and urge those i mentor to just go ahead and replace the tank with a new one and even better replace it with a Hayes O ring type tank. Just as cheap if not cheaper in some cases and far superior to the old fashioned type agine a list to long to list in this thread.
How about the engine, you have not mentiioned it yet good to go?