Depends on a couple factors.

First, are you maintaining this old boat as a traditional Chris Craft?? Or
do you just want some reliable engines to go boating with??

Second, what do you mean by 'Shot' or 'on its last leg'.. Have they been
freshwater cooled all these years or is the block rusted through??
(BTW. I purchased a '59 30' Chris Craft that had twin 283 V8 Chev OEM
conversions. Both engines frozen. I tore them down but found rust through in
the cylinder walls.. Purchased new/used std blocks and head and rebuilt
using the cranks,cams, manifolds and reverse gear, etc.) Just like new.

I don't have any idea of the availability of rebuild part for the hercules
engines. I suspect they are something standard, converted by Chris Craft for
marine..

Maybe someone else knows the origan of the Hercules engines. I started in
boats in the '50s and always heard of the Hercules engines but never owned
any.

Repowering will be very expensive with any new marine engine of that size,
with reverse gear is going to cost $4k each. Then you still have to modify
the boat engine beds for them, maybe even new shafts and props.

Good luck Peter

Steve
s/v Good Intentions