I am changing from a atomic to a four speed and my mechanic is telling he has to weld some to the Cross member for the manual? Is there something you have to weld?

Hey, David, I'm not sure about the cross member, but I think you should be careful welding around that atomic transmission.       Sorry, couldn't pass it up!   

OK The automatic transmission. My dyslexia kick in about that time.

David;

There's good news, and bad....
The good news is that your crossmember is fine the way it is.  You just use the four speed mounting plate, which is only available in used, and the rubber mount (about $10) for the four speed.  You also need the clutch linkage, all of which is available.  There is a bracket that welds to the frame for the clutch crossbar. 

The bad news is that you need to replace all the pedal mounting under the dash, which involves first removing the dash.  But it is all doable.

Good luck!
Larry

Well it looks like we are going to weld the tabs for the manual transmission. If you get a cross-member for a 4 speed you have to weld the cross-member to the frame. Seems like that would be hard to do with the body on the frame. Is there any other way to do this?

There is absolutely no need to weld the crossmember.  The automatic crossmember is exactly correct the way it is, and does not need to be welded in place.  Bolting worked fine when it was supporting the weight of the automatic, so it will certainly hold a 4-speed.  You just need the bolt in bracket for the 4-speed.  You cannot weld in the bracket, as it needs to be removed before the transmission will come out.  The only welding you need to do is the little tab under the master cylinder that serves as the outer pivot for the clutch cross shaft.

The only exception would be if you want to re-create an NCRS correct 4-speed car, in which case having the crossmember bolted in is an aesthetic  problem only.

Larry is right on all of this...the auto x-member will work for the 4 speed, with the correct mount plate/bracket.
The only welding needed is for the clutch cross-shaft support on the frame, under the master cyl. area. The engine has the threaded hole for the other end of the cross-shaft linkage("Z"bar).

if you don't have t weld the X member thats a plus, latter on  when gas goes to 25,00 a gal it will be easier to put a 5-6 speed in, you won't have to pull the motor or lift the body  

Its not the cross member that my mechanic wants to weld it's the tabs that are in the middle of of the cross member for the four speed mounting plate. To get a cross member from vette central  with the tabs you have to weld the cross member to the frame. Thats is what I don't want to do. So I guess we will weld the the tabs. The mechanic seems to think that is important or its more time$