Inboard exhaust configuration

[Outrageous]

I have to start with what a GREAT SITE this is and how much great info has been shared by its members. I have owned several boats over the years most of which I have modified, restored, overpowered etc and just beat till they broke. Of them all the SeaCraft is what I have gone back to as they stand out above a lot of others for there sea keeping abilities. I am currently in the middle or hopefully beyond the middle of a 23 SF resto project.
I would greatly appreciate any help or input to configure the exhaust system as there was nothing to go by as I bought a hull, trailer and some parts but no engine or transmission. I have what I believe to be the original muffler (two 4" inlets and one 4" outlet) but was wondering what it had as original for exhaust manifolds and the height of the risers. My plan was to go with center rise manifolds and spacers 3" or maybe 6". I have a 4" heat exchanger I believe to be original Volvo and was hoping to be able to cool the exhaust system with fresh water if possible. I have not been able to find a cooling diagram for this setup (1974) any help locating a source for one would be appreciated. Power is a 350 w/ a 71c B&W transmission.
Thx to all that reply.