Re: aq 171 c rebuild?
The VP AQ 171C (or A) was Volvo Penta's last "real" Volvo engine based on a Volvo car engine (everything since is essentially based on GM blocks).
It is a GREAT engine when it runs, but due to limited number of engines out there, parts are hard(er) to find, and many times horribly expensive (I did not know this when I bought mine, but knock on wood, it's been running fine so far), compared to its simpler sibling, the VP AQ 151 (SOHC) or earlier engines.
The head, timing belt, tensioner, valves, water pump, ignition, are all unique to this engine. Very few automotive parts can be used. The exhaust manifold cost somewhere just south of $2,000, or more than a set of manifolds for a V6 or V8.
Short, it is a pricey little power plant (but was really a modern one when it came out, and sort of still is today with its DOHC and truly electronic ignition w/o points and preprogrammed set-points for different rpms). For its power, it is fairly fuel efficient.
Should I start over, I would likely look at a kit with a VP V8 or V6, or (of course) go with a diesel.
All that said, if you want some AQ171C information, I probably have a fair amount, and also lots of photos of both my set-up and a few over in Scandinavia (more of these engines there, but still not many...). Can of course share.
For 350 information, many here on iboats are true experts. They will chime in.