No because by 86 there were no more BOP 400's, only Chevs in the trucks. Last 'normal' production car to get the 400 was the 81 Cadillac. The 82-85 Cadillac hearse / limo still had the 400 but those were not real common. BOP stands for Buick Olds Pontiac and Cadillac. Chev was the oddball back then.

BOP engine to Chev transmission adapters are made, most transmission specialty places offer them.

Why a 400? The 350 diesel didn't make much power so just about anything will hold up. The original transmission that came behind the 350 diesel was the THM200 which is most likely what was in your 88 unless it was ordered with the towing package then it was a 350. 82 it would have been the 200 4r w/overdrive.

Diesels used a different stall rate torque converter but those should not be hard to find since the 400 was used behind the 6.2 diesels. Just look up a c/k 20/2500 or 30/3500 with the 6.2 for that. The 10/1500 trucks usually had the 700r4. The diesel transmissions usually also had a different 'tune' in em than the gas ones. Flexplate may be an issue. The 400 truck converter used the larger bolt pattern than the typical car transmissions. For Chev engines most of the aftermarket flex plates have both sets of holes. Not sure about the Olds plates. Also not sure if the Olds diesel is the same flex plate as gas so that may be a hard to find piece since it was pretty rare to find a 400 behind a olds diesel. 78-81 it was an option in the c10 trucks. Some of the diesel torque converters used 6 bolts in the torque converter which could be a further complication.

Depending on what transmission was originally with your 350 you may also have to find the proper vacuum control valve that mounts on the side of the IP to control the vacuum modulator on the trans. Most of the transmissions found behind the 350D's were the 200, 200 4r, or the FWD 325's which did not have a vacuum modulator so most of the IP's only had a vacuum dodad to operate the EGR valve.

if the 400 transmission is out of a chevy then it won,t bolt to a oldsmobile ! if the 400 transmission is out of a pontiac or buick then it should bolt to your 350 engine if the 400 transmission is for a small block because a 350 is a small block and the only way a 400 transmission will bolt up is if it came out of a small block engine !

It will unless it is a turbo 400 with a Chevrolet bell housing. Bo explained the other issues.

yes will need to use the torque converter from the diesel also, flywheel might also have different weights so check the flywheels