I now have CAT club headers on my car. Dale designed them and Claudia has been welding them up. They are maintenance free stainless and I have zero leaks. They also tuck up tighter than any header I have seen on the Tiger. It used to be that Sanderson made Tiger headers and they hung below the oil pan so you ended up with D shaped rusted tubes. I used to have Tri Ys on my Tiger and it was a nice set up but you have to have a good exhaust guy to build the lower Y, it’s very labor intensive. As for the rest of the exhaust system I used a local exhaust shop that I like. 2 1/2 diameter pipes seem to work best.
As for installing headers it can be done in the car by moving the engine off the mounts. If you have the engine out, install the drivers side out of the car then the passenger side once the engine is in.