I'd focus on the wall thickness, in the area 1 to 2 inches down from the deck. Measure each cylinder, at at least 4 points. Write it all down. The top portion of the cylinder, is where the magic happens. The pressures are very high there. By the time the piston is 4 inches down in the bore, the pressure is decayed big time.

If you find some core shift, some machine shops, will offset the bore index if you desired. Meaning, if you find .300 on one side, and .230 on the other, they can offset the bores.

For what you're doing, I wouldn't worry about it. I'd prob go with a minimal bore thickness of around .200, unless you plan on spraying nitrous, or strapping a blower on it.

FWIW, on those old Mark IV 454 blocks, .100, or even .125 overbores, weren't unheard of back in the day. But the blocks varied alot, some could go, some couldnt. Just depended on the casting. Thats why ya gotta measure them all over the place to make sure you're casting is consistant.

I'm liking the idea of a 4.375 x 4.350 build (520ci). I think you could make a nice stump puller.

I think it would be a fun and different project.

Funny you mentioned the trick flow heads, i dont think ive ever seen them on a marine engine, but do all the time on cars, wonder why that is?

Probably marketing. Just like on oso, AFR heads are the #1 aftermarket choice here. They are a good cylinder head, but they aren't anything better than you can get from Dart, Brodix, Engine Quest, RHS, Trick Flow, and so on. You can make big power with all those heads, with the combination.

I don't know how they are since Summit Racing bought them out, but I know my head guy really likes their quality. He uses alot of them over the years. Mostly Fords, but some BBC ones as well. I've heard good things about them from other head guys as well.

If I didn't go with the EQ heads, I was looking at the aluminum RHS 320's as an option. They run about 500 a set cheaper than the AFR 325's bare (1500 a set). They come with Tungsten valve seats. The EQ's come with Powdered Metal. AFR's come with Ductile Iron. For marine engines, I myself, won't run ductile seats. They have been proven to simply not last long.

Seems like the bubble is bursting on the huge money bbc aluminum heads

I played with that kind of overbore years ago in drag boat engines, and as stated the thickness were all over the place, have to have the block sonic tested and fine one thats thick, we ended up filling the blocks to make .125 work decent, but in reality, you would be better off with a better sealing .060 than a leaky .125

big cu in 454 for fun,the fun will end when it splits a cylinder wall,lol.

Dont the bow tie blocks have thicker walls, seems I read that you could bore it to coffee can size, dont see many around, must be low production, I know their pricey if you can find one.

Heres a couple builds that used a stock block. One is a 4.5 stroke, 4.310 bore. Other is a 4.25 stroke, 4.350 bore. One had Trick flow 320s, the other , RHS 320's.

All the MARK IV 502's, were "bowtie" blocks. So, in the early 90's, if you had a 502 Mag merc engine, that had the fuel pump on the block, you had a "bowtie" block. Good blocks. Not as good as a Dart, or Merlin block though.

They also made some bowtie race blocks, with billet caps, instead of the ductile iron. I believe the billet cap ones, were rated for 1200hp, where the ductile cap ones, were rated for like 800hp if I recall. According to GM's literature.

Very, early trick flow decal I've had since the late 80's or very early 90's.
The guys were at a big Ford swap meet in Columbus showing their stuff and I picked a couple up.

Good stuff and a good pricepoint.

http://i205.photobucket.com/albums/b...ps4x9o7ibg.jpg