I agree with the above post...
In the earlier years the Regal( Other W Body ) used the 3800 V6 early on while the rest of the W's were using the 2.8,3.1 and 3.4 DOHC.. A 3.8 will fit in the engine compartment just as well as the 3.4 DOHC..
And the Stock M90 Blower will be nestled neatly between the heads... The 3800 Series II and III are all a dime a dozen... Parts are more than plenty and Mods are all there to make a 3800 go from mild to wild or in between..
Lets look at it this way... The stock L36 NA is supposedly reliable to 300 HP... The L67 is supposedly good to the tune of 600 HP, That not saying it'll last at 600 HP... But there are quite a few making that kind of power on a stock bottom end...
and when you get to the series III Bottom end you get Powered Metal Forged rods as opposed to cast..
There are plenty of cams for the series II and III, Rockers... Intakes... PCM's and Tunes... Personally I would pull the 3.4 DOHC and sell it to someone that wants it and build up a 3800 SC...