can i bolt up a Th350 to a LS1

 

Yes, but if you are gonna do a a3 do the TH400. It's alot stronger and isn't a whole lot more than the TH350. Check in the drivetrain or drag racing forum and you can probably find quite a few guys who have done this swap.

 

i heared the bolt pattern is diff

 

Check with Yank there is a bellhousing spacer/adapter you need to have.