Want to modify a 12a header to fit a 13b.I've been unable to find the center to center measure to the exhaust ports as the are wider ,Any help Thanks BT

 

well the 13b housings are 10mm wider each, which is 20mm, but since the exhaust studs are in the center of that 10mm, thats only 5mm per side, so its a totalt of 10mm. i think this is something people mostly eyeball

 

THANK YOU! Faster for free is always GOOD! BT