He's a tad optimistic with the asking price. The rear carrier on the civy bikes was an optional extra, but that's not the correct one. The tank is off a 3HW and the hot cross filler cap is an Indian copy WD type, looks like a strange extension to the filler neck? The knee grips aren't Triumph, they look more like Royal Enfield? The front mudguard is ether repro or post war, it hasn't got the correct rivet set up for the front stay and I'm fairly sure that the P clips on the forks were only for the WD models. The headlamp with srew in top and the ammeter are repro/postwar. Only a picture of the frame number would determine its true ID. All in all quite a tidy shiny bike worth about a quarter of his asking price to my mind.
https://www.ebay.co.uk/itm/PRE-WAR-ULTRA-RARE-1939-TRIUMPH-3S-350-MOTORCYCLE-SIDE-VALVE-ENGINE-swap-swop/132898718638?hash=item1ef16183ae:g:FzAAAOSwv7pb6vXs:rk:1:pf:0
Ron
email (option): ronpier@talk21.com