455 in an '86 LeSabre?

The Olds 307 in my LeSabre Estate Wagon Hearse is starting to age. I was wondering what all would be involved in swapping in an Olds 455. Would I at least be able to keep my Hydramatic 200-4R Tranny? I don't want an 'X-Treme Makeover', I just want more power and torque. The Beast weighs 5000lbs empty, and the 307 was efficient at best in its day.
Jim

Expect ALOT of work. Swapping from a small block to a big block will take some doing, but it's possible.

I swapped an Olds 455 into an '81 Cadillac Fleetwood, which, as you know is virtually identical to your hearse in terms of chassis design and dimensions.

It is an easy swap, especially since your 307 is an Olds engine as well.

The engine will bolt up to the transmission, which is half the battle.
Use 455 engine mounts. You might have to weld them in place on to the existing frame.
The stock radiator will work in the stock position. You would need a new exhaust around the engine. Olds engines used this strange system where the left manifold exhaust runs beneath the engine then sweeps up to meet the right side, so plan on a bit of exhaust work. Consider true dual exhaust throughout, anyways. The stock 307 pipe amd muffler may be a bit restrictive.
Use the 455 accessory brackets. The rest is relatively minor details, such as adapting the 455 carb and ignition to work with your existing systems. Is your '86 EFI or carb. If its carb, its lots easier to work with.

My 307 has a 4bbl Rochester Quadrajet (also in need of rebuild/replacement). I've upgraded the rear exhaust to bigger pipe and Flowmaster mufflers, but Y'd after the catalytic converter (my 307 is pretty restricted at the ports, anyway). What about the harness and the existing 'brain'?