[Healeys] Frame repair advise - 1964 BJ8 Phase 2

[JJSandSMS at cs.com]

Need advise,

Our HBJ8-L/28207, an early phase 2 car is about ready to be media blasted.  
The frame/chassis is totally stripped and is on a rotisserie.  Once blasted and 
primered I need to do some repair work, driver's floor, left footwell, rear 
trunk floor, and both shut pillar face plates (where door latch and front of 
rear fenders attach) will need replaced due to rust.  The frame itself seems 
very solid except for the top of the left rail from the motor mount to about the 
center of the drivers seat, which is rusting from the outside and appears 
thin.  Kilmartin makes a u-shaped frame repair piece that is supplied 4 feet long 
and is designed to fit inside the frame rail once the very top (or bottom if 
desired) of the frame is removed.  That is the area that is 3 inches wide that 
has the weld bead.  The repair piece has 1 inch legs that fit inside the frame 
and then whole thing gets welded in place. 

Question, how and where should the chassis be supported when we cut out the 
top of the rail at that location?  I would definitely assume we would not leave 
it on the rotisserie!  Would supporting the bottom of the frame in four 
spots, two near the front of the car, say between the motor and suspension mounts 
(on each rail) and two near the back of the x-frame be sufficient? Should we be 
concerned with warping or twisting of the chassis as the old piece is cut out 
and the new piece is welded in? If so, how do we prevent this short of 
rigidly attaching to a frame machine which we do not have? We will use a MIG welder 
and certainly take our time to minimize any heat.

Anyone have any experience with this repair piece? Suggestions?  

Are we in over our head with this repair?

Thanks in advance,

Jeff