Quote:
Originally Posted by J-(Chicago)
If you are using the 9'' tail shaft, you may have to move your crossmember, and if you are upgrading to an 8.5'' rear end you will have to get your driveshaft resized. I am doing a similar project this spring. I believe you can use your 307 motor mounts and it will drop in ok. 455 is an inch wider at the intake, but the motors are almost the same size. I'm not sure about A body headers on a G body, but this swap has been done a thousand times, and I'm sure someone else can clarify for you.
The guys on Realoldspower.com probably do this swap weekly. You'll probably find info on everything over there.
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This is pretty much correct. The 455 has a taller deck height, so the engine is both wider and taller than the 307, but the motor mount locations and bellhousings are the same. The 307 accessory brackets will not fit on the 455. Prior to 1980, most Olds brackets were capable of fitting on both big and small blocks, but the 307 brackets are small block only. Note that the brackets, pulleys, and water pump must be a matched set. Olds used different water pump lengths and the pulleys must match.
Be sure to use the 307 motor mounts and frame mounts. DO NOT buy 455 motor mounts, they won't bolt to your frame mounts. As noted above, a TH400 with the short tailshaft will bolt up to the 200-4R crossmember location. Other TH400 tailshafts will require relocation of the crossmember. You'll need a double hump crossmember anyway if you plan to run duals.