Well, my personal rule of thumb for a naturally aspirated street motor is cubic inches times 1/2, so for a 350, 175 is about right. I'd go with the 180 cc heads.

You have me a little perplexed with your mention of changing cams in a couple of months. Normally, a builder would optimize the cam for the static compression ratio that is built into the motor from the git-go. If you make much of a change in the cam, you'll have to change the static compression ratio also unless the motor is optimized for the longer cam now.

What is the present compression ratio of the motor?