Hello,

 My name's Randall. I'm new on here & have never been on a forum before, so please excuse if I post stuff in the wrong place, etc. I've been in & around jet boats all my life sans  the last 15 years or  so............  A couple of weeks ago I found a decent deal (cheap) on a '75 Tahiti 18" jet, so I bought it & viola! I'm back into jet boats again. So this thing has a 455 olds in it. The guy advertised it as "ready for the water". When I looked at it I noticed that a head bolt "head" is broken off. Ready for the water my a**. I have a considerable amount of oldsmobile parts @ home including a ready to run 403 olds. While I have the 455 out to go through it, I was thinking of running the 403. What I'm concerned about is exhaust width @ the transom Vs @ the snail outlets. The 455 is considerably wider than the 403, is it too much for the exhaust hoses to compensate for?

 455's about 3 inches wider. Maybe they didn't cut the exhaust holes for a particular engine, but just in a standardized location?
 Everything else is the same, all of the accessories will match except ski tow rack thing. Heck, even an olds 350 diesel would bolt in there, that would be interesting wouldn't it? I wonder how a diesel would act in a jet with an A-impeller?
 As for the 403, I rebuilt it back in '97. 350 #7 heads & a mild cam. I'd figure 325 hp  375-400 tq. It probably has 25-30k on it but its all late teens to early 20's "hard" miles. It ran fine when I pulled it, just been sittin on a stand since about 2001-2002.

Its overall, so 1.5" per side. Ill update when its in there.

So I'm close to done with the swap.  It turns out the exhaust does cause some issues, but the issues I thought I'd have were ok.
So deck height is a big factor, the water feed to the back of the snail hits the stringers before the mounts line up.

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The other issue was the oil filter relocating adapter,  can't run a ph25 filter, have to run a skinny one. The change in deck height makes the snail interfere with the bigger filter. Whatever the factory number is for the 403 works fine.
There is 1 corner of the adapter that just barely makes contact with the log. A file fixed that. Ill attach pics of that when I get the log repaired.

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