The spline from the MGB wheel will fit a Midget spline and the offset should work ok, but the down side is that to use 14" wheels on a Midget you need a pretty low profile tire and finding tubes to fit might be a problem. Remember the wire wheel rim width is also 1/2" narrower than the Rostyle width, so again tire size is limited. On a RWA car you should be able to fit a 5.5" wide 13" wheel with a 195 size tire without problem and this should give you all the traction you need unless you've done an engine swap. You can squeeze a 205R50 13 and a 7" wide rim in with minimal tire rub if the offset is right on. Unfortunately I can find only one source for this size anymore (Sumitomo).
'73 Midget (V6)
'59 MGA (I6) under construction
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