How much clearance between the exhaust & crossmember?

Hey I am installing my exhaust today and got a Summit kit made for the e-body. I am turning the different pipes and it looks like it will line up pretty good so far. I'm just not sure how much clearance I should leave between the exhaust pipes and the trans crossmember. The car is currently up on jack stands so I'm not sure if things will change much when I set it down.
Also what about the gas tank and mufflers? The mufflers will be pretty close to the tank on either side.