Toby we did an engine similiar to this for a guy in New York. What we did was a 3.250 stroke but we had a big bore block that made a 4.125 stroke and this got us 347 C.I. a different way. We did this engine with about 11 to 1 compression and with the Victor heads with shaft rockers. This engine made a little over 600 HP but at like 7500rpms. He had it in a Cobra and he liked it but it was about a 14,000.00 engine. This is what it will take to make about 475 at rear wheels. To make 400 at rear wheels we would need about 525 and this could be done with a 331 with about 11 to 1 compression, solid roller, AFR 205 heads, Victor JR intake and a nice carburetor. This combination should also get you about 400 to the rear tires. A complete engine like this could be done for somewhere around 9000.00.
The biggest problem with the 347 combination is not that the pin gets in to
oil ring or the rod angles all though it is not as good as a 331, the biggest problem is the short cylinder on the 302 block. If the cylinder was longer at the bottem the piston would not come out of the cylinder at bottem dead center as much. When at bottem dead center the piston rocks quite a bit due to little support till it get back up in the cylinder some, this causes some wear on the piston, cylinder and rings. For longivity we like the 331 better, for racing applications you have the engine down a lot more and this is not as big a problem. I would rather run the 347 with a 5.500 rod to get the piston higher in the cylinder at bottem dead center but this would be a custom piston. Hope this helps a little. Thanks, Keith