rough idle bad vacuum and assorted gremlins

[dey59]

I just bought a 70 gmc engine number says its a 72 model 350 its auto the guy put a hei dist. in it says it has a mild (rv) cam but don't know what it is idles very rough but not like the lope of a cam its erratic I can get the idle down to about 1000 and it will stay running of course you have to get it up pretty high to put it in gear or it dies he says it has a 3000 stall converter in it for the cam I got it out on the road and once you get it moving at 35 or so it runs and sounds fairly well i'm sure theres carb issues I put a vacuum gauge on it and at 1000 rpms (idle) the needle bounces erraticly between 14 an 16 3 of the bolts where loose on the drivers side intake and when I adjust the mix screws theres no change he's got old auto light plugs in it gapped at about 50 also its a 72 motor but the fireing order is for the 75 and later hei does this make a difference I loosened the dist and turned it almost two plugs counterclockwise and it has no effect when it turn it clockwise the same amount it stumbles and tries to die what would be a good plug and gap ac44st or 44str it has a 1405 600 cfm edlebrock which will either be rebuilt or replaced has edlebrock performer intake not looking to make a hot rod just a good dependable truck right now my two main issues are the firing order thing and plugs haven't had time to put the timing light on it what timing specs should I use 72 or 75 and later yet any helped is appreciated greatly thanks doug