Yes, you can usually change the wheel to vend different prizes and also to adjust how many items are dispensed per vend. Try the manufacturer website, Beaver for instance have this information and pricing here -
http://www.gumball.com/beaver-vending-machine-parts.aspx
I doubt more than a handful of machines were ever updated over here due to the cost and the relative difficulty of fitting so many proms.
I've never seen another Plus on site and I've been all over the country looking at the competition over the years.
Deith Leisure were the UK distributors for Midway and Nintendo at the time, they also had their own manufacturing plant in Wimbledon where this machine would have been manufactured.
It's as official as you are going to get over here so don't worry, it's a good cabinet with a game that was built...
I can say categorically that this was an official Sega upgrade and not a hack.
I operated several Scud Race twins and deluxes and later fitted the Plus upgrades personally.
The kits were provided in exactly the same way as the Daytona 2 Power Edition, only through an official Sega distributor...