I have an '87 Buick LeSabre Estate Wagon with the stock Olds 307. She burns oil at a rate of a quart per 100 miles, drips while driving, and the freeze plug is shot. So, I need a new motor.

I have found a '72 Olds 455. I understand this will bolt right up to my 200-4R and the existing motor mounts. My question is, being a taller motor, will it jam up against the air conditioning box or cause clearance issues with my hood with an Edelbrock carb? Also, will I have to go through the transmission to strengthen it to handle the additional 200 lbs of torque?

 

The trans will need attention or it will go boom. As far as fitment you should be alright there. I had a 455 in a 1980 Cutlass on the 260 mounts with no issues with the air box and I'm sure that is a tighter fit than the B body is.
The thing you need to worry about the the AC as it's tied into the computer. There is a way to make it work, but you'll have to do a search of the forum because it's not something that I ever had to deal with.

 

You shouldn't have a clearance issue, but if you do, the 307 valve covers are contoured just a little differently and might provide an extra fraction of an inch. If you plan to keep the A/C, you'll need to weld extensions on the 307 brackets. The A/C cutout that is controlled by the ECU actually opens a relay when the throttle is at W.O.T. If you do nothing, the A/C will continue to work fine, but the compressor will not cut out at wide open throttle. This is primarily an issue of slightly increased drag on the engine, so you won't get maximum acceleration. You probably won't notice the difference.

 

It has been done many times, the B body does have more room than the G body and handles better. You will have to control torque converter lock up with a toggle switch or controller. It may be tight to the heater box, you could use the 307 valve covers. I would also use a QJet or Street Demon 750 over the Edelbrock carb. You also need the correct brackets to use with the 2004R trans TV cable. You will need a good rebuild on the 2004R, I would add extra clutches in the 3-4, all quality Alto clutches and steels, hardened stator, good 10 vane pump set up with the 700R4 pink spring, a good shift kit and servo, a bottom feed filter, deep pan and a billet shaft and drum are a very good idea. It depends with you are doing for exhaust and other mods on how much the trans will need, the billet shaft and drum is a $400 upgrade but a very good idea over 400 ft/lbs. Your 455 will be very close to that mark.