This stuff isn’t wonderfully cheap but you could use something like this?if the gauges are 60mm then they fit in a treat and don't move around at all. I have an AEM wideband to fit but its 56mm so need to find a solution that isnt blue peter haha
CLEAR ACRYLIC PERSPEX PLASTIC TUBE BAR HOLLOW 30mm 36mm 40mm 50mm 60mm 70mm | eBay
You can get it in 60mm OD with 56mm ID. Can make a sleeve out of it to bridge the gap between the vent and your gauge. You could use metal tube which would be cheaper but I don’t know if it would be a good idea to have metal in between two plastic items.