i really, really doubt it.
i know for a fact (used to have one) that the 70's datsun pickups (521 and 620) came with L-16 engines. (datsun L-series engine)
i am not sure about the earlier datsun pickups. (pre-71) i don't know what engines came in these pickups, but i really doubt it was an MG engine.
there is a thread in this forum specifically about these older pickups, the guys in that thread would be able to tell you what motor is in thier trucks.
here is a link to that thread-
http://www.automotiveforums.com/vbul...d.php?t=440190