on my mini the closest thing to the firewall is the inlet manifold (i took a 5mm notch out to clear it), the engine has plenty of room of the firewall, but the gearbox only has about 30mm. To get the engine further back you could always mount it on a slight angle, but that would make the turbo go further forward out the grill.
You could also have problems with the width of the engine, unless you go full flip front with no inner wings, would give enough room for alternator and radiator too.
The mastes arnt a problem as you can turn them around to clear, but if you have to cut the firewall to fit it, then the masters will have to be moved inside. If i was to do a round nose i think id go and cut the front off, tack weld a frame with the engine it and then try to mount the original panels around it. You may get away with just spacing the grill out 40-50mm

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1974 Moke - 998cc
76 Clubman B16a2 Vtec AWD Turbo 12.9@105mph
https://www.youtube.com/watch?v=V9PW49e1hYs