Who makes the best 347 for high reving NA use?

CHP, and i like the parts that Keith Craft uses for internals....thats the only thing that might make me go with KC over CHP, chp uses their brand rods and crank.

How high do you plan on revving the motor? For what you have in mind, id be skeptical about using the stock block to rev to the moon and spray on top of it.

U may want to consider the 331 for "hi rev" use. It has better wrist pin placement for less stress on the cylinder walls. There is plenty of info u can look for that will back that up, 331s rev better, longer, and faster then the 347. Also, u need to let the company know( whomever) that your using TWS TW heads, because not all pistons will work with that design. Stock lifters are good as long as you upgrade your valve springs to handle the lift, may want to get some new pushrods. Also...i recommend a custom AFM " Hi Rev" camshaft...beautiful little things they really are..they come with Hi Rev valve springs...

But if you really want a 347, i would use the stock bore, 4.000, and have yourself a 342. The extra beef around the cylinder walls will give you added strength in the long run... U could get away with using a new stock block, they can handle 7200 rpms, just keep the HP realistic..500+ is a no no...