What size cam do I have in my 340?

I am trying to figure out what size the cam is in my '71 340. I built it years ago and it has never run very well (low vacuum, rough idle, etc). I know its a purpleshaft but can't find the original box or receipt. I measured the lobes and got the following: top to bottom 1.556". Side to side 1.225" It has stock rockers. So does that mean the lift is (1.556-1.225)*1.5= .496"?

That's about right, and probably has a decent thump to it.

Replace with a medium Lunati VooDoo cam and you'll be pleasantly surprised.

It's either the .484 or the .509 cam and both of those are much happier with a race setup where they never have to idle below 1000 rpm.
R.