There use to be an absolute pipe bending guru that lived in my area & made headers & mufflers for about 90% of the race cars & boats here in Australia, but he retired..... He made good 4-1 headers for me at $350Aus/set.(a decade ago). He use to let me buy bends & collectors from him dirt cheap too, I tried not to bother him too much.

Also of interest, We never saw an advantage in 4-1 over 4-2-1 until we spent a day on the dyno trying different mufflers. No turbo type muffler was any good & we found only one specific type of straight through muffler that was good with 4-1 headers.