Thanks Chief.
I made a die to fit the round tube in the oval port. I took a pice of scrap and milled an oval, then used a slitting saw to split it in half.
All I had to do was form it in the vice.
I was pricing out headers on a 351 swap for my 83 Mustang and was a bit shocked by the price and limitations on primary size, so I decided to build my own.
before tacking them up, I used masking tape to hold the primaries together.