I went down the road of very long primaries (1.5" x 28") baffle collectors then short secondaries (1.75" x 12") then a merge collector to a 2" diam. tailpipe.
Info for these dimensions is from "Four Stroke Perormance Tuning" by A Graham Bell.
These pipes perform like 4 into 1`s but with more midrange.
Cost only $280 in 316 stainless mandrel bends and tube. but about 30 hours of work!
A15, 271deg cam, hi comp, 500mm intake runners and injected.