One of the biggest mainization costs is a wet exhaust manifold.
This is claimed to help lower the engine room temperature and allows a wet exhaust.
My preference is dry stack, but if a wet exhaust is required
Custom Marine Inc. - It's All About Performance - Header Applications, Tailpipes, Accessories
and others can supply a wet section for an exhaust.
Marine Exhaust Systems of Alabama, Inc.
www.[B]mesamarine[/B].com/
http://www.mesamarine.com/
The stock manifold gets a riser , drops down and then the wet section is installed.
Any number of sources will sell a lace on hi temp insulation kit for the exhaust manifold to your specifications.
Hopefully good engine room ventilation is part of the swop, most stock boats stink at providing enough air.
The fewer "marine" parts the lower the cost.
IF you are willing to go outside the box , the international 360 and 466 (6 cyl inline) are built with electronic timing , or straight mechanical.The boat choice for under 1000 hours a year.
These are smooth quiet engines that are sold at remarkable low prices with minor use.$3k to $5K and all have SAE bell housings so the TD tranny is easy to fit.
Many working lobster boats and others that can use 100-150 Cont hp have discovered these robust engines.
With a good used T/D the installation could be under $5K to 8 K complete.
While a good auto wrecker can provide a late model engine with few miles , the best I have heard of is a Skoolie bus takeout.
The Feds allow the skools a new bus every 12 years or so , however the highway funds are also robbed for ongoing maint.
At the 10-11 year point many will receive new engines , as therre "free amnd the mechs find R&R very easy and profitable.
Purchase one of these at auction and for a grand or two you have a nice new engine , and all the electronics if you prefer the fuel saving of the black box.
Boating only needs to be expensive if you must Strut The Dock , and do not have some mechanical skills.
FF