At the very least you'd be looking at a Manta or Carlton gearbox. This question, if you reeeeeally want to pursue it, would be better directed at a website where people use Astra engines such as a Locost / Lotus 7 replica website. As David said, it is highly unlikely that anyone has ever done this to a Minor because anyone planning a re-engine probably wouldn't ever think of using an Astra as a starting point.
There are some interesting engine transplants on here if you have a look around. Zetec, Suzuki, Rover V8, Biiiig V8 etc etc. When I was 21 I put a 2 litre Fiat Mirafiori twin cam into an MG Midget. Even doing it all myself it still cost more than the original car to convert it. How big is your budget?[frame]

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