the lowest recovery you have is probably for alpha kits / XeDK. which is why it says that. each console only goes so low
if it says the hw is incompat if you built it manually i still doubt it would boot, although thats weird. my XNA kits take recovery 7978.
It's been a while since I did anything with 360s, but that doesn't look like a Xenon GPU. It looks like the 80nm GPU out of a Falcon with the smaller DRAM die. It's obviously not an Opus, since it has the ANA chip rather than HANA - but if this was an MS internal board it might have been one that was assembled with the new GPU for testing purposes - which would certainly explain why the old dash won't work on it.