These engines are truly amazing. I have bought two from Scale Production and am in the process of installing one in a Fujimi GT40 MkII, attaching the gearbox to the rear cross-member using two RB Motion aluminium "bolts". Getting the gearbox to fit correctly was not too difficult but the engine itself is a tad long, requiring work to clear the main rear bulkhead and although I didn't want to I have move the seats forward 3.5mm to clear the ancillaries on the front of the engine.
I have also bought two pf your 289 Cobra engines from MBW, one of them is going into a DDP GT40 Roadster - it used the earlier engine with the vertical carbs, not the later Gurney-Eagle engine with the inclined carb's.
Oh and I have four of your GT40 Mk1 engines, they fit in the Fujimi kit much easier because the gearbox is not so bulky.