Ok.....this may be a dumb question, but I pulled my 455 olds and putting 454 chevy in my jet boat. Ok so the olds had Hardin motor mounts on it and I bout guardian motor mounts for the chevy and just replaced the hardin feet with the guardian feet in the existing spot where the hardins were. the question is am I going to have to redrill the stringers or is the 455 and 454 going to mount up the same? Like is one going to be longer than the other mounting up?

Ok.....this may be a dumb question, but I pulled my 455 olds and putting 454 chevy in my jet boat. Ok so the olds had Hardin motor mounts on it and I bout guardian motor mounts for the chevy and just replaced the hardin feet with the guardian feet in the existing spot where the hardins were. the question is am I going to have to redrill the stringers or is the 455 and 454 going to mount up the same? Like is one going to be longer than the other mounting up?

The chances of that working out are about the same as my ability to fart a fresh crisp $20 bill....  

I would be more than a little surprised if it was even close...

Plan on re drilling and re aligning virtually everything, like rigging a new boat...

GT

Ok.....this may be a dumb question, but I pulled my 455 olds and putting 454 chevy in my jet boat. Ok so the olds had Hardin motor mounts on it and I bout guardian motor mounts for the chevy and just replaced the hardin feet with the guardian feet in the existing spot where the hardins were. the question is am I going to have to redrill the stringers or is the 455 and 454 going to mount up the same? Like is one going to be longer than the other mounting up?

Many of the vintage polished cast aluminum mounts (Hardin, Harman, Guardian etc ) were all cast in the same foundry and from the same tooling (simply had different insert "plugs" for name changes) and work with very similar crank center line to base of pan measurement . If the cast mount feet use the center spine/rib (versus the retangle type eg Glenwood) you may get lucky on the stringer hole positioning . The mounting position from Olds to BBC is very close (feet to stringers only) As you probably know there are no other bolt pattern simialrities for example on the bell hsg circle. Ironically with some work a BBF rear mount can be reworked to fit BBC  Call if you need help Tom