hey, I have a 86 Cutlass supreme with a 307.

when i have the money, how hard would it be to swap in for something bigger.

i would like to go bigger than 350.

Any tips?

 

It's pretty much a bolt in either way. With a BBO you run into some exhaust issues that you otherwise wouldn't with the SBO, but it's not all that difficult to remedy, just a bit pricey depending on what you do.

 

Check to see that if the heads were about 1" farther away from the crank the brake booster, etc. would clear and you could remove the valve covers. There will be a lot of G body guys and conversions on oldspower.com

 

As noted, a 455 is about 1.5" taller than the small block Olds, but many have been swapped into G-body cars with no problems. You either need to use the 69-72 W/Z exhaust manifolds or the special (and pricey) headers for this swap. Alternately, a 403 Olds is externally identical to the 307 and bolts in directly with no issues.

 

I had a 455 in my 78 regal (and will be putting it back in with a fresh rebuild soon) and had no problems with it fitting in but had to use 307 valve covers to clear the A/C box. I modified sbo headers to clear the frame and made a 3 u-joint steering shaft to clear the headers. I hear if u use exhaust manifolds u have no issues with steering shaft. Its not hard at all!!! oh ya the 86 cut and 78 regal r the same under the hood

 

307 valve covers are the same height as any other factory Olds valve covers.