458 had a strange existence, spending July 1941 to January 1942 in Yorkshire, coded FU-, then being sent to the Middle East, safely ferrying out 36 Wellington Ic to Egypt. Before the personnel arrived, their aircraft were issued to other Squadrons, and the aircrew posted elsewhere. 458 "re-formed" (though it had never been disbanded) in September, 1942, and flew Wellington Ic VIII, carrying MD codes. The marrying of aircraft to crews needs a look at the Operations Record Book (O.R.B.,) which is held in our National Archives, in Kew, London. There is always a problem with checking the ORBs, since the comprehensive (or otherwise) nature of the entries were entirely dependent on the amount of energy which the allocated (rarely a volunteer) officer was prepared to expend; I've seen serial nos (often,) code letters (rarely,) both (like hens' teeth,) nothing whatsoever (thankfully rare, also,) so you just never know. If your grandfather flew in BB457 it was MD-U, and HX519 was MD-F; others might be in the ORB, but it's pot-luck. I often visit Kew, so, when I get a chance, I'll have a look.