I assume that the instructions for your Holley heads don't say anything about it? I have TFS TW heads and they have a nice procedure write-up on how to check for proper pushrod length in their instructions. I followed them and had success.
Here is a
link to the instructions. It's covered under section 5.
This may at least give you a basic understanding of steps involved. It worked well for me - I just took my time and had a few cold ones.
Hope this helps.
E