Hay Blue,
I took my '72 302 to a local muffler shop & had them install new tubes (& the cheap "flowmaster/turbo" look-a-likes) from the exh. man. back.
The tips exited behind the rear wheels. The whole job installed, for under $200.
It had a nice mellow sound at, & off idle....& didn't rumble in the cab at speed.
Headers...really don't come into play 'til higher RPM. I guess they're all pretty much equal. (some req. a cam change)
Carb/intake swaps can cause hood/air filt. clearance issues....& additional expense.
A clue would be your intentions.....street & mild trails, then leave it stock.
Pit racing, then lift, big tires, big carb., headers/cam, turbo exh.
Rough & tumble rock, then get your wallet out...
OH YAH,.....there's a great article (including "H" pipe) on exhaust in the JULY issue of 4 WHEEL & OFFROAD ....Page 90 thru 95...!
HTH
B