For those of you who did the timing and AFM mod, I'd like you to check your fuel trims via VF1 and VF2 grounded to E1 under the diagnostic cap.
Standard range is 0-5V. Ideally, you should see 2.50V, which is optimal and means that the fuel trims are +/- around 1-10% (closer to 2-3%).
5V is too lean
3.25V is lean, but within range
1.75V is rich, but within range
0V is too rich
Obviously, not as easy as OBDII, but if your reading is above 3.25V, you should definitely make an adjustment either with more fuel or by turning the AFM back.
Also, larger exhaust pipes does not equal more power gained as it can reduce exhaust scavenging. More than likely, the current exhaust pipe diameters (read that carefully) aren't a restriction. Rather, the manifolds are as they're a basic design.
A y-pipe mod nets some of the biggest gains if you remove the T intersection and smooth the exit of the rear bank's flow into the front bank's pipe.