I got my 331 dynoed yesterday.. 289 rwhp, 272 rwtq.
I thought I'd be over 300 on both for sure.. The dyno was a Mustang unit which I heard gives lower results than other dynos. Some info on my engine: Holley 4150 with vac secondaries, RPM Air-Gap, AFR 185, compression ratio ~ 9.5:1, COMP Cam 280HR (mild street/strip), MSD 6AL, mechanical water and fuel pumps, TKO 600, 3.77 diffy.
On a positive note the car is more responsive. I can definitely feel the difference. I gained 21 HP and 15 TQ over the base line due to rejetting and adjusting the timing but it cost $500! What do you guys think?