From the announcement:
LaserCutCard has released an “imperial” upgrade kit for the generic APC.
The upgrade kit includes a turret with autocannon, decorative scrolls and decorative eagles.
It also includes a hull mount that will fit a GW heavy bolter or heavy flamer (which are not included).
It is available as a single model or as a pack of 3.
Worldwide shipping for the pack of three is under $5