Your diffs should be the original versions. AFAIK only the new 811 buggys come out the box with V2 diffs. I'm pretty sure desoto means 500k for V2 and 300k for V1 diffs.
Stock setup is a good start and go from there.
Billy Easton is probably who u want to talk to regarding buggy but the Man U want to talk to for the cobra gt is Desoto JR. Seen him this past weekend run at the GLC and he killed it.
On the same track but not prepped my fast laps are low 22's while he has no problem consistently putting down mid-high 21's lap after lap.
Would love to know his setup for that weekend but didnt want to bother the guy lol