You might want to make the Proctor a long term project as it takes patience...not difficult, but not to be rushed either. Would make for an excellent electric project since the dummy engine would not be in conflict with a recip.

I think the Proctor would not be my first build. 

 Mike

Whatever the volume of fuel… consider it all bad vs suffering downstream loss of engines and existing models. Glow fuel draws water from the atmosphere.

Look for a Spektrum battery “station”. This is going to be larger than what you would expect to find for a transmitter. I suspect from what you described you will find the operating instructions with it. All batteries “must” be prequalified before any consideration for actual in model use. 

Your BIL appears to have been more organized than most if he were a hoarder…which it does not appear to be the case as it appears he had quality...not simply quantity.

I recommend you join the club with that field and seek the assistance of a club officer to help navigate through this stash. In general it sounds like most of it is in hobby shop inventory new in box. I would be cautious of selling blind of an item’s true value. Too often an estate inventory is treated with less than true value and falls victim to great loss.

Typically eBay could be a quick value gauge…low and high with a virtual instant result.