The MGB uses a 4 by 4 1/2 bolt pattern.(ie. 4 bolts in a 4 1/2" circle)
This same pattern is used by several American and Jap cars.
Partial list, and by no means complete or inclusive.
General Motors: 60-64 chevyII, Corvair
Ford Motor Co : 70-75 maverick, 60-67 Falcon/Mustang, 61-75 Comet
Chrysler Corp. : 71-75 Colt
Japanese : Datson 510,240Z,260Z,280Z; Toyota 1600 Corolla, Corona MK2,
Before invading the wrecking yard, take a measurement of the back spaceing
on the MGB wheel (measure from the inner flange to the flat surface where the
wheel mounts on the drum) Then check the back space on the spare you select
from the wrecking yard. DO NOT accept a wheel with more back space than the
B. A bit less is OK