360 la headers & straight pipe

You want it louder? Remove the exhaust and replace it with 2" pipe, preferably mandrel-bent. More compression would help quite a bit, but smaller pipe is both louder and more obnoxious-sounding.

Every obnoxiously-loud truck around here is 2" straight pipe on a low-compression '90s 5.7 Chevy K1500 or 5.4 Fjord F150. The Fjords are louder due to higher compression.