No, the NC431V is not an official model – but it’s a hell of combination: a 2-stroke NS400R engine shoved into a modified NC30 chassis, all wrapped up in NSR bodywork.
Unfortunately, the seller barely has any information to share and I’ve struggled to find additional info myself. It appears that a company in Japan (possibly called Auto Staff Suehiro but their website is no longer up) created these conversions back in the 2000s and that a total of 17 were made. Here’s a video of #17:
I’ve also seen photos of a Telefonica Movistar replica and an Antena 3 (Spanish TV channel) replica. A thread on Aprilia Forum seems to mention this bike back in 2011 and suggests that the conversion cost about 11k pounds (now roughly $14k).
All the seller says about this example is that it’s #1 of 17 and it has about 1,000 miles. Oh, he also helpfully adds that it’s “rare.”
Find this custom Honda for sale in Poitiers, France with a classified listing asking for £31,500 ($40,439) or best offer here on eBay.