Also to help with flats use Stan's No Tubes latex based sealant. This stuff only adds a few grams of weight but will save you a lot of time and frustrations with flats. All tubulars have a removable valve stem,
Liquid sealants for tubulars have been around for at least 30 years. Mike Fraysee sold a brand of tubulars with the sealant already installed. I tried out a pair on the GEAR 1977 ride. The rear flatted about 20 miles into the century and the front about 15 miles later. The only difference over tubulars without sealant that I detected was that in addition to gluing on spares and pumping them up, was that I now had gobs of a rubbery substance on the seat and down tubes that were the devil to remove. I also had some of that stuff up the back of my jersey for good measure.
Others have reported that the efficacy of tube sealants is inversely proportional to tire pressure. I would not recommend such sealants for narrow profile racing tubulars that are inflated to 100+ psi, based on my experience.
BTW, there are still tubulars sold without removeable valve stems.