We began with two lengths of tube, 120" long, a few inches longer than stock Model A rails - the tube is supplied in 24' lengths, so we also had a four feet long offcut. You have to start at one end or the other, and as the front taper and curved frame-horn were to be basically as original that's where we started, the shape being marked out on each side of the rail.
A line was then marked out offset 3/8" (10mm) from the bottom edge of the tube on each side. This was the cut-line for the lower face of the rail, which would leave the full radius of the tube on the bottom edge, and still be easily curved to match the new profile. Then a line was drawn offset the same distance up from the bottom curve of the taper. The front tapers are just under three feet long, so two cuts each side of the two chassis rails total over twenty feet of hacksawing by hand, three inches each side at a time!
The edges to be welded are ground to give a good chamfer for weld penetration, then the rail clamped down onto a heavy (straight!) beam. Steel plates are clamped either side of the tube to align the two sides of the joint, then the bottom face clamped down to follow the curved profile. A number of tack welds are made at various points along the joint, on both sides, then the welds are finished in roughly 3" runs. These alternate from side to side, and are made working back towards the previous weld, leaving gaps that are filled on the next pass. By completing the joints in stages, allowing some time for cooling between each set, distortion is kept to a minimum.
A MIG welder was used as it combines ease of use with the ability to deposit a lot of weld filler material. The excess weld bead is ground flush, then the top curve of the front horn is produced in the same way as the bottom (a lot less hacksawing though!). The frame-horn is capped at the front by cutting in half a piece of 2" diameter tube, then welding the bits onto the open tube ends. A 3mm thick disc was made to fit snugly inside the end cap, and tacked to it before welding to the rail. This doubles the wall thickness at the rail end which leaves enough material to grind a radius of about 1/4" to match the rest of the tube.
To finish off the frame-horn, a slice is taken out of the inside face to produce the open section, tapering back to where the cross-member will be mounted. The whole process is repeated for both tubes, taking care to produce left- and right-hand rails! Also note that the face with the tubes' weld-seam (visible in the photo above) is towards the inside of the chassis, leaving the smoothest face showing on the outside.