Replacing chassis tube: Barlotti mid 70's.

[911hillclimber]

I am almost ready to buy a Barlotti class 4 chassis that is quite butchered at the very rear for seat frames/supports and aero struts from a dark past.
I like the idea of bringing one back from near death.

Did Barlotti use seamless tube for the chassis and braze the tubes everywhere?
Do you all use brazing as opposed to MIG welding for these relativly unstressed areas?

Is it easy to find plans of the chassis to get the original dimensions to get back to the right form of the design?

I am no stranger to restoring cars and race cars.

Hope you can help (and in the furure!)
Graham.