I'm sure that you know that SE's (Google, especially) penalize for identical content on different sites. Therefore:
1. Make the content SLIGHTLY different!
2. Use different domains (you've already got that).
3. Use different IP addresses (that'll reinforce the SE's belief that they are different domains).
4. Get a "serious" client as the above can be accomplished from the same database BUT you'll need to code the slight differences in the theme or after fetching the content from the database. Moreover, changing to a WP-based website means:
A. That you'll lose the ranking of your HPAS website (unless you're REALLY good at retaining URIs - or 301 redirecting all the important URIs) and
B. You MUST keep WP up to date as there are regular exploits against WP that, if you don't update immediately upon a patch release, your website will be insecure (and likely to be hacked).