Header fab question

I am going to build some headers for my 64 D100. My question is how can I get the 2in tubing to fit somewhat tightly into the header flange? (at the head). I am using DOUGS flanges and the have a large rectangular opening as most BB headers do.
Is it just a matter of hammer and weld? or is there some shaping tool Im not aware of. thanks for any ideas ahead of time.
Tony

i think you're going to have to be creative with the hammer & make so wooden dollys to help shape the inside. i used Hookers flanges & they came with stubs so it was easy to add onto.

Hmmmm

I thought we had this conversation







I did it , you can do it !!!

I use STAHL flanges. They come cut to fit the size tube you are using. I squeeze in one direction (for the long side) with a vise down to the height measurement of the flange hole. Then use a good "C" clamp to squeeze in the other direction (while keeping the long side in the vise) till you get the other measurement. Fine tune with a square body hammer on the flat of your vise. If done properly, it will just fit the hole. Practice on some scrap stubs first!

RIP

Port match your flange to the head and stick your round tube on it .It looks better, helps out on reversion ,and you are going from a small hole into a bigger hole . No point in pounding your square peg in a round hole.

We just make a mandrel just undersize of the flange port,tack the round tube at the flange,heat it,smack the mandrel in from the back side of the flange and tack some more,once it's shaped weld it up.Any gaps fill with weld and radius with a pencil grinder.

Wasnt me , I had headers but they dont quite fit, so Im making my own. Thanks you all for of the ideas