hiya soviet1942
looks like standard allen key but probably not metric might be imperial which will be slightly diferant in size.
All bolts on engine will be imperial (UNC or UNF) but bolts on bus will be metric.
Bit of advice i got from the corvair centre forum, you realy need to seal engine in bay to obtain proper
cooling and prevent heads getting too hot which could cause valve seat to drop, this had happened to mine when i bought it.
there was at least a 6inch gap all around engine.
I've done it on mine just manufacturing steel plates to fit, make some cardboard templates then transfer to steel, made some that fit to engine then filled gap from body to these and used some old pop top seal between to two, also, made some deflectors for the engine outlet flaps otherwise the rear bumper got very hot to touch.
hope this helps as its good to see another bus with corvair power.
cheers Peter