is a 340 interrnal or ext balance if so what should the flywheel be i have a nuteral balance does it need to be balanced

Early pre 73 internal balance. 73 up external balance

340s are internally balanced and use neutral flywheels with the exception of the 73 340. it is externally balanced.

its a 73 so is the flywheel nutreal or do,es it need holes drilled in it if so where and how much

The flywheel must be drilled. Where or how is another question. Sometime ago the tech archives of this web site had an excellent blueprint of where how large and how deep but I have not seen this in sometime, I do not know why it was removed. Wish I could be more help!!!

Take it to a machine shop or better yet a clutch rebuilder and they should know what to do. Also check with Autozone they have one available for $69, don't know the quality.

theres nothing wrong with the wheel just need to no how much ballance

Any 340 with a forged crank is internally balanced; any 340 with a cast crank is externally balanced. Most, if not all, 73's and some late 72's had cast cranks.

Yours might have a forged crank if it's an early 73, OR if someone swapped in a forged crank some time in the last 35 years.

Check the harmonic balancer. If it has an offset weight on it, your engine is external balanced. If not, it's internal.

Can't help you on where to drill the flywheel to make it external balance.

IF you have a cast crank 340 the damper will also have "Use with cast crank 340 only" cast into it.

Just wondering here. Could you buy one of those B&M offset balanced flex plates and install it between a neutral balance flywheel and crank???

Yes, it's been done.
When the first chevy 350 strokers were built using the 400 crank there were additional sheetmetal counterweights that you could bolt between the crank and flywheel. Didn't seem to hurt anything.

The diagram for the flywheel drilling is in the MP chassis book.
R.