Call Stahl and talk to Judy......I went through the same dilemma as you.......I decided to go with a new motor with W-9's and an alterKation so I could get headers to fit.
There were other compelling reasons too , But I looked into the Stahl headers for it.
I believe they are under the car.......or at least not full fenderwell.
The odds are that at least one tube will be outside the engine bay just based on how much room is available.
There will be some tube cutting maybe , and getting them to fit will be a treat.
I had the Hooker's with the 1 5/8 primary on the car and they were an exercise in patience whenever they went on or off.
But I am going to use the later A body with 1 7/8 " primaries and they sold me the tubes pre bent and a set of collectors for a great price.
I was told that some of the tubes will need to be cut and welded on install for the p/n 303 's.
The options are limited for under chassis.
TTI makes a set in 1 5/8 to 1 7/8 step headers that looked pretty good......I think one of the torsion bars had to be removed for install.
Good luck with it.