1977 michigan 75b loader

I have a 1977 Michigan 75b loader s/n 443a317fsc, someone put a v555 engine in it and kept the v504c flywheel which they had to oplong a mounting hole to make fit. The loader has a very bad vibration and is shaking the machine a part. I do not think you can use this flywheel with this engine. does any one have a solution do I need to find another 504 engine? could I repower it with a 5.9 cummins and if I do can I use the same flywheel and bell housing. Thank you for your help

1977 michigan 75b loader