This is a problem I ran into on my first transplant. I took steps on this one to move the PTO end mounts as far forward as possible to help with this. If your PTO belts do not have a spring loaded tensioner you can easily increase the load on your motor mounts 2 to 3 times their rating.
When the belts are engaged extra weight is put on the front end of the engine due to belt tension.
Yesterday I was able to complete the fuel system and some more of the wiring. Tomorrow if nothing comes up the battery compartment will have to be fabricated so the wiring can be completed.