Heya Roger, First of I hope you have a wonderful time during your fundies. It's a hard course but in my mind there is no course that opened up my mind to what is possible in diving than this little gem! No matter what else you have planned in your diving future, it's a range of skills that will make all diving more comfortable and enjoyable, IMHO.
What I would suggest, is even tho it's not so easy probably in your woods to find gue trained buddies, is to already start diving the gear that you acquired. The more familiar you are with it, the easier it will be to use during the course. There is a lot of stuff to take in during the course, and if you at the same time need to adjust as well to a lot of new gear it's going to be of course tougher. Specially a doubleset I wouldn't use if your not using it in any case during your regular dives. During my fundies a while ago (2010), one of my classmates was using a doubleset, cable light and drysuit for the first time during the course... he "fought" more with his gear than with the skills taught... he's know I believe GUE's most recent addition to the instructor corps and will teach in France ;-)
Regarding equipment, I like your pragmatic approach, but rest assured that all GUE instructors will not force Halcyon gear on you (if they would I'm sure the would be in violation of the code of conduct), they probably will advice on some of it, because it's just good gear. A big part of the fun in standardization is not in equipment but in procedures, but even in gear it can come in handy sometimes. In 2015, my car was broken into on my way to doing cave dives in France. I continued to the cave diving area without any gear, but managed to do some very very decent dives using only spare equipment from all the buddies around in that area... For an instructor, part of the organisation and management of the course is also the logistics surrounding the course. If some equipment breaks down, or if something is forgotten, he will most of the time try to repair or use spare equipment, this is just easier if he knows that all are using gear he is familiar with.
PS: While I don't actually own that much halcyon equipment, my wings are all halcyon (40 lbs, 60 lbs, single tank and the rebreather wing)... because it's just very good gear.
PPS: You'll find that most instructors are very approachable and more flexible than you would think. When I did my fundies we didn't even dive nitrox (just air) because there was no adequate filling station in the neighborhood who would supply nitrox.
Good luck with the course! I'm sure you'll have heaps of fun... and write a report when you are done!