I would have recommended getting a new combo booster/master cylinder from an American car, but you already have a new master cylinder.
In my case, I have the opposite, a Nissan booster and a Ford master cylinder ($30 any day).
Can you measure the overall diameter of you current booster, so a new one will roughly have the same size and you avoid some body work to the recess done in the fender well. Also, the distance between the mounting holes for the master cylinder. I think that with whatever booster you choose, you'll need to do some new fabrication for mounting it to the body.
I borrowed a picture of your engine bay and lightened it a bit, so others can have an overall idea of your setup:
Minion Missile brake booster.jpg
Another solution could be to install a remote Bendix Hydrovac, connected to the front brake lines only. That way you can install the master cylinder in its natural placement.
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