tuning help needed

Ok guys I don't know what big blocks like but I'm sure there are some here that do. What's going on is a fellow moved near me and has a Challenger with a 440 in it that sounds mean but is a slug and has asked me to help him get it running better.

He helped build it about 15 yrs. ago and said they put in 10.5 to 1 rated pistons but didn't deck the block or check the height they sat at so it may only be about 9.5~10 to 1.

Has a 284/484 purple cam.

Has 906 heads with a little bowl work and a 3 angle valve job.

1-7/8" full length headers with full length 2-1/2 exhaust.

An old Direct Connection aluminum dual plane manifold, not sure what it really is, i.e. part number or ??, it just looks like a low rise aluminum dual plane.

750 vac. secondary Holley.

Has a factory dist. with a MSD 6al.

2500 stall and 3.55 gears and 27" tall tires.

I think I remembered all the specs he told me but if I missed something let me know and I'll find out.

In my opinion it should run real good but I guarantee after riding in it the thing would be lucky to turn 16's.

Ok now the question. What do you guys like to see for a max timing on something like this? I checked it and right now it's 12 degrees at idle and 38 total all in by 3000. I think it probably needs some more initial timing but what do you think? Also what total timing do 440's usually like? And if any of you guys run a 750 vac. sec. carb on a dual plane intake on a 440 what jets are you running? How about a plug suggestion and what gap??

Oh yeah, I put a vacuum gauge on it and it pulled 11~12 inches of vacuum at idle.

Thanks for any help you can give. Tracy