Since you are still on the cam selection part, might I suggest a stock off the shelf cam? It is a Compcams Magnum. 282s solid lifter series.
It is .570 lift, 282 advertised, 236@.050, 63 degrees overlap. It is a 110 center with 4 degrees advance built in so it will do better with a low restriction exhaust system like even stock in a Pantera but doesn't really need an open exhaust.
I have this cam and mine idles down nicely once warmed up to 775rpm and gives me 17inches of vacuum at idle. It seems to peak at around 6500rpm but will go as high as you want.
With these timing features it will work in a automatic transmission without too much issue at all. All cams seem to be some kind of a compromise and the compromises on this one aren't bad and you need to look for them.
This one works so well, why do you need to go to a 113 center if it makes this much vacuum? I don't see the reason for a custom cam?