Balancing Question

[cantbeatpar]

I have a 1972 boat. The previous owner told me it had the original 305 in it, but the manual says its a 307. I changed the motor and installed a 350. I have been told that ALL longblock chevy motors are internally balanced except the 400, So i used the harmonic balancer and flywheel from the old motor. Now im being told that if it was a 307 it could have been externally balanced and if so my bearings and seals wont last a year. I could really use some clarification on this matter. The old block has been exchanged already so i cant access any numbers from it. I was told by an old chevy guy that the 307 had an oil fill tube up front by the water pump and the 305 fills through the valve cover. Is this acurate? Should I be worried about this balancing issue? Is there anything else i should know? Please help!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!

[five7kid]

307's are all internally balanced, as are all factory SBC's except the 400.

'86-later SBC's have a one-piece rear main seal, which requires a flexplate with a weight attached to it. However, they are still considered "internally" balanced.

For a little history, the 307 first came out in 1968. It was the baseline V8, replacing the 283. It had the same stroke as the 327, and the same bore as the 283. It had valve cover oil fill cap, as I recall, part of the PCV incorporation that replaced the road draft tube as the means of venting the crankcase.

So, no problem using the 307 damper on the 350.