I did some research on the 3800 Series II a few months back.
Basically, it is a whole different engine from the old 231. Only the displacement is the same.
However, there are two versions sold in the States, the regular 3800 Series II, and the supercharged version found in the Grand Prix GTP and Bonneville and a couple other cars.
According to what I could find, the only difference internally between the two is the pistons and connecting rods. The supercharged version has forged rods and dished pistons. The supercharged versions also have slightly modified heads (fuel injectors are stuck into the heads on the supercharged version, NA version has the injectors in the intake manifold). Valvetrain is a very nice roller setup, and cam is the same for both versions.
The pistons and rods were like $650 list price new from GM here in the States. According to GM, the 3800 Series II with the dished pistons can take 12 psi of NON-intercooled boost without knocking on U.S. 93 octane pump gas. The only reason Pontiac isn't putting Turbo-Regal power down with this plant is Cadillac won't let them have a transaxel that can survive under that kind of power. They don't want their front-drive DOHC Northstar cars trumped by a 12 valve pushrod V6.
Converting your NA 3800 to turbo would be a relatively simple matter of replacing the rods and pistons, fabbing some manifolds, slapping the turbo on, and tuning the fuel with something like an S-AFC
