John, you wrote this in an earlier post:
"The ITB cars with essentially the stock exhaust port are getting 150 HP or more at the crank with 4 -1 headers, though not necessarily in a power band appropriate for the street, so it looks to me like improvements in power are possible up to that level with the right exhaust system."

Would you or anybody else know what dimensions the ITB guys are using for 4-1 headers?

Cheers,
Paul.