never actually thought about using different headers

got to be worth a look into
but there are so many other variables in exhaust design, that even if you find a set that fit [at a push

] you will probably find the sonic tuning aspect will be shot at least
as for funds, we all have that issue

but I would check breakers first
ask specifically for after market headers off a Thunderace
as they don't HAVE to just supply OE kit