EZ, just run a 1/8 mounting plate with 273 port sizes. It will give the 340 header O-ring flange something to seat on. Much easier than welding, just use a 273 gasket as a template and use a jig saw or plasma cutter. the Cyclones were built before 68 so their ports are 273 sized. will need 2 gaskets per side. I had the same port mismatch on a set of Hookers : 340 head ports on a 318 header flange and the entire bottom was unsupported..didn't help that the mounting holes were drilled too high...Hooker asked for a receipt (refused help when I could not come up with a 4 year old $550 receipt) when I mailed them the gasket showing them the port mismatch due to holes being mis drilled. How's that for a lifetime warranty on manufacture defects?
