That's where I was going next . . In my area there's about three guys who can build a set of headers, although they're not "Lemons" or anything of that grade . .
OR . . . You can put the heater and A/C evaporator someplace else . . . 53 thru 64 Studes had the heater under the right front seat, as did the 55 through 58 Pontiac . . The '46 through about 1963 Rolls Royce Sedans had their A/C Evaporators in the trunk . . All of which involves fabrication, but of a different kind . .
In my own case, because there's not much room for access under the dash of a '34 Ford once you stuff an A/C unit under there, my eletrical panel is under the back seat cushion and the windshield wiper motor is behind the Right Rear Seatback.
When you have to have room for HP, there's other places for all the gingerbread!