You probably have an answer already, but I recall making a couple of sets of four cylinder long-tube headers back in the day, from cut-up V8 header sets. I would buy a set of SBC truck headers, then cut the tubes apart into J bends so that I ended up with a whole bunch of curve-straight transition pieces. Then it was a matter of measuring the length of each of these pieces, starting at the head flange, and working my way to the collector and to arrive there with four tubes that each had the right length. It would take about ten to 12 hours of work to get to a fully welded header.
Given the tube size of these Tiger headers and the overall lack of space to work in, I can't imagine it taking any less time per side, at least for the first time around. Subsequent iterations might save a couple of hours because the fabricator would already have a good plan of attack... but I think you'd have to be ready to pay for a lot of shop time to get headers like this.