I had a 1995 22 Scarab and put a ZZ-502 in it. Ran a 27" Mirage and would do upper 70's if you had the balls to stay in it. Chine walked after about 70. You could drive through it but you had to stay on top of it. Definetly couldnt hold it for long at these speeds. Up to 70 however it was rock steady. I had Eddie Marine exhaust with the tail pipes to minimize reversion. The boat really needed external hydraulic streering with all the chine walking at speeds. My current boat has it and I can tell you I will never go without it again. Never had a problem with the engine mounts. My boat came with a 454 so it was designed for big block torque.
Good luck and be safe. Bring her up to speed slowly to see how she feels.