duel exhaust conversion

[thunderbolt]

If your 289 is relatively stock, I would go with 2 1/4 inch exhaust all the way back. If you have modified it quite a bit, 2 1/2. It it were me I would go with tri Y or long tube headers, and put in the cross over (H Pipe). This would give you a healthy exhaust, support preformance improvements, increace power and milage. So muffler sizes would be determined by exhaust size. You can go straight through mufflers, I believe offsets are a bit quieter. Don't use glass packs. Muffler technology has come a long way.