Ok, having modded and used both here are some facts:
Both are simple two wire hookup. One wire goes to the coil "+" and one to
the coil "-".
Both units have a vacuum advance can attached.
The Hitachi (from 1983 Nissan Sentra) works fine but it is a tight fit. The
cap screws on and must be removed to pull the dizzy. Part of the housing
must be machined (or filed) down but the OAL is good from the start. The
drive dog uses the same pin hole location on the shaft but the hole must be
enlarged. The shaft is the same diameter as the Lucas shaft. The shaft
doesn't protrude beyond the drive dog like the stock Lucas unit but this
doesn't really matter. I think it would work well in an MGB application.
The Isuzu unit (Nippon Denso? I think, from an 80s P'up 2.0L IIRC) is
smaller, has a snap on cap, and looks more at home in the Spridget engine
bay. The case mods are a little more involved as you have to shorten the
OAL of the base about 1/4" or less, maybe and remove a little metal around
the ring for the Spridget clamp. One could easliy rig a clamp mechanism
similar to the stock Isuzu clamp. The shaft is longer and must be shortened
and a new hole drilled for the drive dog. The shaft is slightly smaller
than the Hitachi and Lucas shafts, but not enough that I felt a bushing
would be necessary. The stress involved in turning the shaft is low enough
that the fit should be sufficient. I didn't measure the shafts but I could
if anyone needs to know the difference. Another plus to the Isuzu unit is
the advance mechanism is similar to the Lucas mechanism. You can increase
the mechanical advance by removing metal. You could then decrease the
advance by bushing the advance stop. The Hitachi advance mechanism is a
little more difficult to modify.
Both units functioned fine. I got the Hitachi on ebay for $5 plus
shipping. I had to pay $30 for the Isuzu at a U-pull-it. Caps and rotors
for both are around $12
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