When installing Subframe connectors i know that a lift that you drive up onto is best because it puts all the weight on the chasis as it would be when your driving. But the shop im talking to about installing them has a chasis lift and there pretty much isnt anywhere around here that has a roll on lift. So how big of a difference will it make?

 

Find a shop that does wheel allignments, the suspension needs to be loaded when they do those, so they should have a roll on lift.

 

If you (or actually the shop) are brave you could put the car on blocks to load it. I think I would have some jack stands positioned closely too though!