I made a new page, that can be found here: https://wargamer-eric.ca/horus-heresy-extra-unit-rules/ (it will be at the top bar) to list the old 40k rules for units that can be used in 30k. I have updated their old rule entries to match the 30k style and fluff. All the actual rules are the same.
There are also the 30k pamphlets I made you can print and hand out :).
I will be adding more later. If you have any other things you would like me to add let me know!
Example of the rules: