98 Silver Bullet

iTrader: (28)

I'm swapping from a 3.8 to a LS1. Is the bolt pattern for the transmission the same for both?

Nine Ball

iTrader: (38)

I would bet they are identical. GM is pretty good at making transmissions interchangable betwen their different engines. For example, a TH350 or Powerglide will still bolt up to an LS1.

Tony

Speartech

iTrader: (14)

Unfortunately the 3.8, regardless of what vehicle it is in, uses the GM front wheel drive style of bolt pattern. It's completely different from the LS1.
We have used these transmissions for Northstar rear wheel drive conversions.

98 Silver Bullet

iTrader: (28)

So, if I had the standard, I could use the transmission, but since I have an auto, I have to get a new one, right. Which would be cheaper a 4L60-E that fits, or converting to a standard?

Speartech

iTrader: (14)

If by standard, you mean the 5 speed that backs the 3.8, I'm not sure how you would use it either. Maybe someone has an adapter plate or something. I have not tried that type of conversion. I would think grabbing a 4L60E that fits would be the way to go.
There are a few that have made the V6 to LS1 conversion here I think, maybe they'll chime in with more info.

John