289 to 351w

The overall width isn't much more than an 1" wider, and should still fit within the engine box with those manifolds, unless I wasn't sure otherwise what you meant regarding "between the manifolds". Regarding the prop, it's exactly what 64Skier alluded to. You CAN use your existing prop, which will make it jump like a rocket of the hole, but you probably won't be able to open it up without turning the engine too many rpm, and thus limiting your top speed and hurting your fuel mileage all the while. Are there pictures of that '64 Skier and the 289 H-M on The Site yet?

I have an old 289 H&M that I rebuilt, bored etc etc. One thing that may help you is that we put a high rise manifold on it and it still fit under the hood.

The point made earlier about the prop probably has to do with the increase in HP and Torque and if so, then you can cavitate the prop when starting out.

Rob,
The 351 is slightly wider and taller, and you probably have the older "hump in the middle" engine box like my '70 Mustang. Hopefully your 351 is a marine unit and a reverse rotation like the 289, or you'll have some other more involved issues. The newer-style center-rise exhausts, if you were planning to use them, will hit the underside top of the engine box as mine did even with a 302, so use your existing if they're still good, or some other log style. I verified with Woody that you otherwise won't have a problem with the width and the box, and that your mounts will bolt up the same and at the same width. He suggested however, that you contemplate new PCM front mounts as the old Interceptor style (or is it a H-M engine)do wear out and eventually allow the front of the engine to drop slightly. I've seent that first hand with mine. The 351 only weighs about 100 lbs more. The 351 will also want and need to spin more pitch in the prop, so plan on correcting or most likely changing it. Call me before you buy a new one. Then hold on, and let us know how she runs. You'll be zooming past 50 with ease.      

Ron,
Haven't slipped a 351 in a late 60's, but in a '76 Mustang. I can't be 100% sure, but I can't see any issues if you have the ENTIRE 351 marine engine. We purchased a 351 long block and then had to pull everything from the orig 302 that would fit. But several items I recall we had to acquire, such as the oil pan, the distributor, the intake, new/bigger carb, etc., and there may have been more. This was a bigger, heavier, 17' Mustang and it would fly, but this brings me to the question of if you'd really want to lose the great 289 unless it's beyond repair, and if you have a complete 351 for next to nothing. You can build ample power into the 289 as cheap as you can convert to the 351. But without knowing what your current availability status is, it's hard to say. If you have to do rebuild, and were just desiring the add'l cubes, then a stroker kit to stretch the 289 to a 347" is readily available, and the prices are coming down daily. Then you get your cubic inches and maintain your original size configuration and no one knows you've got the extra cubes, unless you tell them, and you don't have to purchase the 351 specific items. Let us know what your situation and plenty of 'Fans will be willing to help you out. And my take is that if you love the boat at 45 mph, you'll go crazy over it at 55 mph. Night and day difference.