There was in the end no great secret to welding the chassis tubes on my v8s, just a lot of thought and care while i was doing it.
I must say first that anyone attempting to do this MUST be very good at mig welding and have a good welding machine,
one of those £100 gassless jobbies just won't do it.
I did all the usual unbolting such as
tunnel,
exhaust,
floor to chassis bolts,
seat belt anchors
and the good old handbrake linkage,
On mine I unclipped the wires on the clutch pipe and checked during the jacking up that no other wiring was over stressed.
I removed the petrol tank for safety reasons along with blocking up the pipes and disconnecting the battery.
Undo the steering universal joint and your about ready to start lifting.
Get 4 smallish trolley jacks and 4 pieces of 18mm ply cut to the shape of each footwell bearing in mind that all you are trying to do is spread the load.
Make sure they are not too close to the rails as this will hinder the mig torch.
Place the ply on the two rear footwells supported by two jacks and lift either side up about 3".
Place the other ply and lacks under the front footwells and lift about an inch.
Go to the rears again and lift another 2".
Then the front another 1".
Then jack the rear until you can get 2 pieces of 4"x4" timber resting on the chassis above the diff.
You can then go to the front jacks again and raise them until resistance is felt.
Then all you have to do is cut off the old tube with various angle grinders and carefully fit the new tube.
When the tube is fully ready you can hold it in place with ratchet straps and welding can commence.
The fitting of the tube will be very difficult for someone not used to this type of work because,
where the tube meets the rear outrigger there are several complicated angles to cut and the fitting of the seatbelt bracket is crucial.
I hope this is of help.
Charles.