So I have a 98 MC with 146k miles on the 3.1 and I have read the https://montecarloforum.com/forum/en...67-swap-14610/ thread.

I want to go with the naturally aspirated engine instead of the supercharged due to the different class restrictions at the track. Another reason is because I have a 99 LeSabre with a strong, low mileage 3800 Series II engine and transmission, however, I am not sure if the transmission from a 99 LeSabre is the 4t65HD transmission or the 4t60e. A tree fell on it squashing the roof in but the car is still in great mechanical shape. From what i have read in a few other places online, Monte Carlos and the Grand Prixs are W-body's and the Buick LeSabre is not. I still don't fully understand all of the differences but I know that the suspension and brakes are not the same. My question...would it be a good idea to use this Buick as a donor car for most of the parts or does it have many more differences than if I was to get something like a wrecked Grand Prix with the 3.8 or similar?

 

It's MOST LIKELY a 4t65e. I don't think GM put 4t60s with 3800s after 97 or 98. But I would assume it's the same setup that goes in a Bonneville. Do some research, but I'm pretty sure there are some things that need to be modified to get it to fit properly. You'll probably need to custom build axles (unless you can use 98-99 Z34 axles). Good luck.