318 time improvement
its hard to say, it will deffinately help, but you won't get the full potential unless you get some decent compression... i'm assuming since you said stock bottom end, its probably in the kerosene burning range lol. do you know how much comp. you have now? the 302's will add some. i dunno bout that 60ft. with a 2800 stall and 3:91 sg you outta be better than that, i'd say your givin up at least a tenth right there maybe a little more. i'd say by the specs on that herbert cam your running, it me be a little much with your current setup, but it probably wouldn't make much of a difference (if any) if you went a lil smaller.. ur givin up alittle e.t with that carb too, good choice by goin to holley.
i'd say properly tuned your lookin at about low 14's, i really can't see the swap pulling out over a second of e.t, but you never know. i think it all gonna come down to what you final c/r is before and after the swap, you would be surprised at the difference between 8:1 and 9:1 with good worked over heads and cam, it might not be as noticable when stock, but the more heads,cam, carb, the more that point of comp. will help. but if you get low 14's a decent shot of juice will put it in the low 13's easy... and thats still impressive with 318 c.i, and basically mild parts.