Re: 4.3 or 5.0 Repower
I swapped a 4.3 out for a smallblock earlier this year. Yes you need a little more room forward. Otherwise,
The wiring harness will work - I'm using the wiring harness from my 4.3 on the v-8
The distributer body in my v-6 and v-8 have exactly the same part numbers the caps, are different.
The ignition module is dfferent - has a different advance curve. You can pick up a used one for very little, and if you take a good look at the advance curves, the v-6 has it's advance come in earlier - and is sometimes used for a v-8 build intentionally for the more agressive advance curve.
The alternator, powersteering, etc.. brackets should all work or at least mine did.
If you've got the room forward for the engine, moving the engine mounts forward is trivial. You have plenty of room to do it based on your pictures of the points where the mounts bolt / screw to the stringers. I attached the complete mounts to the engine, set it in place and bolted the rear part up, aligned it (all while still hooked to the hoist), then marked where the new holes should be, picked the engine back up, drilled the new holes, filled the old with sort of runny epoxy-based peanut butter, installed the lower half of the mounts seaing the long lag screws with 5200 and then put the engine back in and put everything else together. Note that since the engine mounts are located to carry a targeted portion of the weight of a car engine and transmission. They actually move forward less than the additional 4+" difference in length between the two engines. I don't remember right off the top, but I think I had to move the bolt holes a little under 4 inches.
The closest area in terms of clearance in my case was the top of the powersteering pump with the front of the engine compartment, it is close but worked out fine. Definately check the pulleys and pump clearance. Although, if the boat came stock as an option for a 5.0, it's dimensions would be the same as a 350 / 5.7 and you should have little or no problem getting it to fit.
The difference between the v-6 and v-8 exhaust is the connecting elbow between the risers and y-pipe - everything else after the manifolds is the same (The manifolds are different of course). They're cheap and easy to find since so many people swap to through hull exhaust. I put two pairs of the elbows, y-pipes and assorted exhaust clamps and hoses on the curb last weekend.
As an aside, if you go with an aftermarket aluminum exhaust on a v-8 it almost makes up the difference in weight between the v-8 and v-6 engine packages... as in within 30 pounds or so by the time you're done.
if you live in Eastern NC, I've got a bunch of stuff for a 350 you can have - I gave someone else my remaining 4.3 stuff aside from the spare engine I haven't gotten around to selling. but if you wind up putting a pre-vortec v-8 engine in it, you (or anyone else quite frankly) would be welcome to v-8 parts: the oil pan (I used an oversized circle track variety in the rebuild), valve covers, heads (1.94/1.5 valves) factory cast 4bbl manifold, etc...
The outdrive gear ratio will work fine...
Don,
I've learned a tremendous amount from your posts and really appreciate the depth of your experience and knowledge. I also agree that overall, Merc does a darn good job of engineering their products. That being said, the notion that a 1.84 gear ratio cannot be used effectively on a v-8 is silly. Merc set up their standard packages for various reasons, many of which I don't know, but there are many good prop options in the ranges that the original poster would have if he left the standard 1.84 gear ratio in his boat with a mild 350.
If for example with his new engine and a 1.5:1 outdrive ratio he would be turning a 21" prop, engine rpms of 4800, theoretical speed 64 mph (add some slip and we're at mid to upper 50's speed, very reasonable assumption for the tyupe of boat we're talking about). In fact, the 1.84 ratio will give more torque at the propshaft and the same peak horsepower (at a lower propshaft rpm). That same set-up with a 1.84 gear ratio and a similar designedand a generally analogous prop design would give similar performance with a 26" prop. a little less holeshot and a little more top end all other things being equal, but just like at any other common pitch range, tweaking pitch, specific prop design, blade cupping, vent holes, etc, etc, etc... can overcome and be set up to optimize whatever performance characteristic are desired. There are alos a lot of common, all-around great-performing props in that pitch range: laser 2, mirage plus, bravo, turbo 2+2, and a host of others... respectfully submitted...
Hope this is helpful.
