OK, now which vacuum can is on it. If he added the HEI to a crate engine, he might have already used the right can. Look down between the vacuum advance can and the distributor cap. You can see the "arm" of the vac advance can where it goes from the can into the distributor. It will have numbers/letters stamped on it. Report back on what it says and I can tell you whether you should change the can or not.
This is the location of the numbers:
