Just tried using the contact at the bottom of
https://www.alteredcart.com/support.php?section=contact
Then I received the following email in response:
I do not think an existing customer should have to buy support points to ask about an upgrade.
I am currently using one page check out on X-Cart ver 4.1 and I am planning to upgrade to X-Cart ver 4.3 all I would like to know is when will there be an upgrade for one page checkout to ver 4.3 of X-Cart. I see ver 4.2 is supported.