I didn't replace the heater core. Have heard of only one leak - Larry Bible did his within the last year. So I wouldn't worry about it.

I don't remember any foam around the heater core. Guessing that it was completely gone on my car! Sure didn't miss it. Nothing rattled.

Took me about 20 hours total to replace the evap and vacuum elements. Sounds like you are on track for the same.

- JimY