I replaced my stock Carter AFB with an Edelbrock 600 cfm performer series carb (on my stock 326). There were two heating tubes that came out of the manifold and into the Carter. These were metal tubes that were compressed on the ends where they slipped into the holes in the manifold. They were held in place only by the fact that they were stiff and fixed in place by their attachment to the carb (the holes are not threaded).
In the picture ( LINK TO PICTURE ), you can see the holes just below the choke linkage. I've added a big yellow arrow for reference
