walt:
cant really tell from your avatar but it looks like your 340 is vintage late 80s, early 90s??? if so and you have a Quicksilver 5.5 - 7.5 series, you have a nissan engine coupled with a generac generator. the engine was used in the early to late 80s generation nissan march and nissan micra, a tiny little car sold only in europe. it is a 987cc engine. i contacted warshauser electric and they were very nice. but they wanted $90 for spark plug wires and $27 for the belt. i bought wires for a 1985 nissan pulsar with a 1.6L engine (i picked this car b/c it is the smallest engine nissan put in any car sold in america in the 80s). each wire measures about 1 inch longer and they perform admirably. cost = $23 at autozone. i took the belt into RS Strauss auto and the gal matched it up to one she found on the wall of belts in the back. cost = $7. granted, certain components (heat exchanger, control panels etc.) cannot be had at auto parts stores, but my philosophy is to save getting ripped off the occasion when you have NO OTHER CHOICE.
btw, this is a great little engine that has been tried and true and proven for more than a decade in europe. it's a shame it is so difficult to get parts for it and that mercruiser has washed its hands of their product. not sure what went wrong there, but talk about abandoning your customers!