Small Change to CubeCart V4 & V5 Payment Gateways

I have a fully functioning payment gateway for CubeCart V4 except there is one small issue that needs fixing : If the paying customer is from the USA, then the county / state field needs to be changed from free format text entry to a dropdown selection field containing all of the US States. Then, once a US state has been selected, instead of passing the county / state field contents to the payment gateway as is currently happening, it needs to pass the standard 2 letter state abbreviation. I have had this exact same work already completed for the CubeCart version 3 copy of this gateway and it works perfectly, so this can be used as a reference if required or you can do the work from fresh if you prefer. For anyone that knows CubeCart this is probably a couple of hours work at most. I will also require the same functionality adding to our CubeCart V5 version of this gateway and will add this as a second separate milestone to this project for the successful bidder