Hi, Sorry to hear about your engine problems you are having. Just as a FYI thing I had read some place some one saying the 470 is kind of hard to get out and put a V style engine in it's place. I went and found it for you and I copy and pasted it for you, See Number 6 mainly. 1. If very well maintained, they are fine. Good power to weight ratio.
2. Like any marine engine, ... if neglected, they will need parts and work.
3.
470 parts are rare, expensive and working on a
470 is tedious and finicky compared to most other car derived units.
4. If one has a choice between a
470 and a common car derived e.g. 4.3 Chevy, go with the 4.3 or a Chevy V8 where complete manifold/riser sets can be had new for $400, and starter motors are $59 etc. etc. and all are available in stock at multiple places online and in your town
5. If the history of the boat is unknown, (i.e. "project"), avoid the
470 due to points in number 4 above ^^
6. Repowering a
470 boat with another type of engine is very difficult due to unique transom plate and with twins, the cutouts may be too close together to ever put vee engines in. Also here is some history about your engine.
http://www.sterndrives.com/470information/470coolantleakrepair.html