Years ago I had great results with the OS 46SF ABC running an 11x8 APC using
Hatori headers and Hatori 7.5cc muffled pipes. Used both std and "wrap around"
style headers- I dont recall pipe length, just with Hatori I never seemed to need to
tweak header length from stock.

Although not a direct comparison for 46's, my friends and I did experiment with
OS 61's and YS 60's on pipe brands. It was no contest- simply by swapping from
Mac's quiet pipe to the Hatori 650 pipe the airplanes flew better- the Hatori was
visibly better. This was done same day, back to back flights on several different models- an Atlanta, Tipo and Avanti.

Maybe on the common auction site or RCU you could scrounge up a Hatori pipe & header
for your 46. If not possible investigate "Just Engines" in the UK and check out the
"purple pipes". Possibly a Hatori clone??

Let us know what you find.

Scott