I agree with Andy. Have you checked to see if the timing belt is properly in place? You could also eliminate the alternator and A/C compressor by removing those belts and try to turn it. If you did use a 924 turbo engine temporarily, the addition of your Carrera intercooler and a modest boost increase would give you better than than stock 924 turbo performance.
You have a very special car, I hope you can find a way to fully repair the damage.
I would love to see it some day.