The 3878 runs a little lean and usually has to modified. I believe the 4164 is what Vans supplies on the 360 currently, runs better with the ram air used on the RV.
Lots of discussion on the forum regarding this. Had to mod my 1995 RV-6 and over the years modified several 3878 carbs for friends to meet 4164 specs. Originally vans shipped the 360s with the 3878 and some years ago went to the 4164 if my memory is correct.
You might want to delete your duplicate post on this subject??