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Old 09-25-2010, 08:32 PM
70Velle 70Velle is offline
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Default 307 to 350 Motor Swap

I recently inherited a 70 chevelle. It only had the 307 block with frozen pistons so I choose to put in a 73 35o. Should I purchase 350 frame and motor mounts to ensure a positive match and easy swap out? Also had a 2 speed powerglide, but going with 350 tranny as well, any adjustments need to be made or will it slide right in. Will post pics later.
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Old 09-25-2010, 09:33 PM
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Derek69SS Derek69SS is offline
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The 350 will bolt in just the same as a 307... For the TH350 I can't remember if the driveshaft needs to be shortened or not. I did that swap in a '66 a few years ago, but can't remember if I had to do that. It bolted in just fine, but I had to modify the shifter linkage. I don't know which style of linkage the later PGs have, so you may or may not need to do that.
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Old 09-26-2010, 07:36 AM
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Hank70SS Hank70SS is offline
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Like Derek said the engine is an easy swap. You don't need to change the frame mounts, just make sure you use engines mounts for a 307.
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Old 09-26-2010, 08:07 AM
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Quote:
Originally Posted by Hank70SS View Post
Like Derek said the engine is an easy swap. You don't need to change the frame mounts, just make sure you use engines mounts for a 307.
Hank is right, I learned that lesson the hard way.

Why did GM make the frame mounts and engine support different for a 307?
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Old 11-14-2010, 10:12 AM
136ED 136ED is offline
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I swapped a 307 with a '78 350 in a '72 and it bolted right in, didnt have to change any mounts.
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Old 11-14-2010, 09:24 PM
BillsCamino BillsCamino is offline
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A short tail TH350 is a direct replacement for the PG trans...bolts right in and uses the same driveshaft.
As mentioned...simply reuse the 307 motor and frame mounts on the newer 350 engine.
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Old 11-15-2010, 07:55 AM
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As far as I know, the difference between the 307 mounts and the 350,400,396,454 etc style mounts are the height. The 307 uses the taller style frame brackets while the rubber cushion that bolts to the engine is shallow and non-interlocking. The HD mounts use a shorter frame bracket and thicker rubber. If you are going to be putting some serious power down you could convert to the 350-up mounts. otherwise, you will be fine as long as you keep the components matched. When assembled together they are both the same height. If you are worried about the engine comming loose and don't have the money for the new mounts you could always make a limiting strap for the engine. I've seen some factory style limiting straps too. They are in case the engine mount rips since there is nothing to retain it.
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