To make a long story long, but not too long, I have a 1985 Merc 305 2bbl in my boat. I may be able to get a VERY good deal on a Merc 350 Mag complete engine (pulled from a boat that had a rotting transom). The 350 Mag runs strong - the current owner says it would be a 1987-1992 vintage based on the "plate" (which i assume means he cross-refed the S/N, i can double check this). My boat has an Alpha one drive, as did the boat the 350 came from.

I've already gone round and back in another boating forum about the merits of doing the swap. For several reasons, i plan to do it IF I can expect a fairly easy "pull out/ drop in" compatibility of the two engines. As the 350 is the complete "fully dressed", as the seller says, engine, does the fact that mine is a 1985 and the 350 is a 1987+ make a big difference?

Again, I realize that i shouldn't expect huge performace increases, but a better hole shot and just "some" on the top end is abig difference for me.

Thanks for any info on the mechanics of the proposed engine swap!

If the 350MagMPI is also from an Alpha drive boat and you are truly getting everything bolted to it (starter, manifolds, risers, ignition, fuel/water separator, fuel pump and cooler, I mean EVERYTHING) then it is as easy of a swap as you can get. Unplug the big black plug, unhook the starter wires, remove the out drive, remove the rear mounting bolts, remove the nuts from the front mounting bolts, unhook the fuel line from the water separator, unhook the water inlet hose that comes from the transom, remove the exhaust hoses from the riser, and lift it out. Drop the other in it's place.
(I am sure I forgot some hose or wire somewhere, but you get the idea.)

Just to add one last step: Make sure you re-align the engine before you bolt on the drive. Use the newer version of the alignment tool. Grease it; slide it in; shift the engine up or down as needed to fit easily reading the grease marks as you adjust; rotate the engine 90 degrees and check again; another 90 and check; and again, and again. There are enough sets of detailed instructions around, but you get the idea. Good luck and safe boating. Hy

I changed a 21 ft cuddy cabin I had from a vintage 1981 305 to a similar early 80's 350 (mercruiser MR1 sterndrive) --- I reused some parts -- and added new ones elsewhere as needed. There are no real issues -- checking alignment is recommended -- I checked mine -- felt it was close -- and ran it the next two years with no real issues -- it was running fine when I sold the boat -- it was as close to unbolt == remove == replace and rebolt as you can get -- there were no real hidden tricks or issues. The boat was defintely better with the new engine -- but an old boat is still an old boat -- the old hull running surfaces were still old designs ---

I do not know the details -- I am sure some Chevrolet V8 people know more than I do, but these is some issue with keeping the years close so that the coupler and starter and all fits -- something about the real seals and such -- perhaps someone know those details better ---

Back around '85 sbc's went from a two piece main seal to a one piece. This doesn't have a whole lot to do with anything bolting up. If you get all the accessories, that would be good. Some acc holes on the heads were positioned a bit different.
When swapping around small chevys, one of the biggest things to watch out for is the internal/external balance, oil pan configurations, vortec heads and bolt alignments on intakes, and accessory bolting. You shouldn't have any problems with this.

The change to one piece rear main seal was in 1987. And that is what necessitates a different coupler and starter. And that's why I ask him to make sure he got Everything on the replacement motor. As long as its accessories are bolted to it, it will slip right where the other engine vacated.

Years ago I did the same re-power in about the same vintage 19' runabout. The actual swap was very easy and straight forward. The only issue I had was with the increase in power because the boat was originally set-up without power steering. While under a full throttle acceleration, the old cable steering set-up was not strong enough to over power the torque of the new engine. Under normal driving conditions the steering performed adequately but I still felt it was a dangerous set-up and decided to add the power steering. The addition of power steering solved all the problems and was very nice, but it also increased the overall cost. The additional power and drivability/reliability of the MPI was nice once completed.