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Old 10-11-2018, 12:56 PM   #3
Mike C
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Join Date: Dec 1999
Location: Austin, TX, USA
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Re: Swapping a 307 for a 350

Quote:
Originally Posted by Warrens69GMC View Post
As long as the crate 350 is 85-under, you are good to go.
Warren is absolutely right, but to clarify in detail: In '86 GM switched to the one piece rear main seal that removed the rear counterweight. Any V8 after that point has an externally balanced flywheel and a different bolt circle so they require the new style flywheel. If you have an aluminum seal adapter on the crate motor behind the flexplate, it is a one piece rear seal block so you will have to find a later style flywheel.
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