that's a great start Bobtile congrats
a spare power-valve rated at about 1/2 of what you vacuum @ idle is,
example 10in. vacuum use a 5.0 - 5.5 Power-valve or 12in. use a 6.0 - 6.5, I like to side on the fat side .5 up from 1/2
{or block it off & go up about 3-4 jet sizes, not really recommend if your going to drive it on the street much}
I'd also suggest that you or anyone doing this type of deal, especially for track use & different weather or elevation conditions,
get some assorted accel. discharge pump nozzles {squiters} & assorted accel. pump cams too,
Nozzles a couple sizes up & down on the nozzles {hollow screws too, better flow} & a selection of different colored accelerator pump cams...
maybe a 50cc Accel. pump kit cam, pump, diaphragm & arm for the front bowl
& jett extensions & a appr. style float for the rear bowl, so it won't starve for fuel on hard launches...
what metering blocks does the Holley 850DP have now ?
that might be something to look into also,
a good set of billet metering blocks with adj. emulsion & air bleeds...
I Like/prefer Quickfuel stuff, but there are allot of them to choose from now...
you know I'm going to say it too...
I'd highly suggest you get a book or DVD on tuning Holley style carbs...
even watch some of the tuning tips on youtube or on Holley's ewebsite
But you know that already thou...
have fun & good luck
- - - Updated - - -
need to make a clean hard pass after you get it close, make a hard run shut it down clean & don't drive or idle around
so you'll get a good/accurate plug reading to see where you are.. will help with the jetting for wherever your racing that day