[curtis73]

Its a B-body. Swapping to a 455 (provided its an olds 455) is super simple. The only external difference between small block and big block Olds engines is deck height. You may have interference with the hood and the valve covers may contact the brake booster, but that can all be measured first.

The motor mounts are the same, oil pans interchange, and all accessories bolt up directly.

You'll run into extreme difficulty finding a 700r4 with the BOP pattern. You'll either have to run an adapter or scour the internet to find that very rare transmission. My suggestion is to spend the cash on the 200-4r and build it up. There are some common misconceptions about the 200-4r. It is not designed to take massive torque (which is unfortunately what your 455 will produce en masse) but as far as a high-hp thrashing they are far stronger than their 700 cousin. Much stronger input shafts and a better valve body contribute to higher stock line pressures and a much longer clutch life. There are companies like Raptor that build 200-4r trannys to take well in excess of 600 hp. There are three other benefits of the 200 family; better gearing by far, lighter weight, and the lockup converters are a much better design than in the 700.

If you're not going to do any neutral drops and drive it like a civilized human, the 200-4r is the clear choice. If you need it to survive in towing or consistent high-torque applications, I might consider an adapter on a 700.

If you visit sites like B&M or Transgo they have pages listing all transmissions and their dimensions. The nice thing about GMs and their engine/tranny combos is that the frames were the same. If you look at the frame around where the tranny crossmember mounts you'll probably see several holes designed for the other trannys. That car as a Chevy Caprice used either a th350 or a 700r4, each of which were different lengths. Same goes for motor mounts. The crossmember would be drilled for either Chevy, pontiac, or olds motors.

You may also want to consider not ditching the 307. It is a factory roller cam. Its weakness is the 7A heads and pathetic intake. Get some 5A heads, maybe headers, a mild Lunati roller cam, and an edelbrock intake and you're looking at a pretty mean 5.0. I'm also not a big fan of the Olds 455. Long stroke and small bores hurt air flow. It will obvioulsy make more power than the 307, but it will also suck down a lot more fuel to make the same power.

Have fun and let us know how it goes