Slant six over heated and now will not keep an idle.

A few days ago I was in a pinch and running late to work I had no other option but to take my 67 valiant to work about a 20 minute drive on the free way. It over heated getting there, after work it was cooled off but when I started it, it would no longer keep an idle. It die's out as soon as it can. I thought it was the alternator being that I knew it was old and worn out bought a newly rebuilt one today from Penny pincher here in phx. Installed it but still no idol. If any one thinks they know the solution please let me know. Slant six car one barrel carb