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Dear Tom...I do take what you said about 307 motor mounts as gospel...my problem is I want to replace a 307 with a 502...so the question is "What is my best way to go?" Should I buy some different frame mounts, have mine altered, get different pieces for the engine side of the mount, or what? Hoping you have some ideas that will work. Thanks in advance. R. B.
 

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All you need to do is locate a pair of 350-454 frame brackets and you are good to go. Then you can use the 350-454 engine mounts for ANY V-8 installation. Check the TC For Sale ads, or, place a Wanted ad. As I said, the 307 brackets are all by themselves (why, I don't know). You can, BUT IT IS A REAL HEADACHE, change the frame brackets with the engine in the car. It is best to change the brackets with the engine out and the front end jacket up so that the lower A-frames hang down as much as possible (and then, it is still a pain). When you get the 307 brackets off of your car, throw them in the garbage, don't save them! If you EVER wanted to put the 307 back in, you just need to use the 350-454 motor mounts!

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Tom Parsons
 

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I hear from every one that 307 mounts are not the same but....I had a 3/4 ton pu with a 350 that I yanked and a 307 dropped right in
. Not saying that none of you guys have a clue but what gives and whats different??? Maybe I'm special and for once things acually worked for me but no one else....I guess I just burnt up my good luck for the next 10 years....
 

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The 307 frame and engine mounts are a different design than the 350/454 ones. I believe that they are taller and wider. They do not interlock (frame mount with engine mount)- as do the 350/454. Doug Flynn's response to a 2/5/99 post stated that he broke 2 sets of 307 mounts with a 350 and a 383. You cannot easily mix 307 frame mounts with 350 engine mounts and vice versa. It can be done but be prepared with a large crowbar(from what I've read in previous posts here). The 350/454 frame and engine mounts interlock resulting in the ability to handle much more engine torque. Yes, the frame mounts are a pain to change out - Iv'e done it to my 72. Using 307 mounts may also bring about header mounting problems due to the frame mount being taller than the 350/454 ones. The part number for the 350/454 frame mounts is 3980711(left), 3980712 (right). I don't think GM would have changed the mounts without a good reason.

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Tino #28 Gold
72 Malibu 350-300,700R4
83 Grand Prix LJ 305
 
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