Unfortunately Griffith Borgeson did not give attention to this DOHC Nagant in “The Classic Twin Cam engine”. Information is very scarce. In “Autorennen” from Cimarosti we find the basic technical data as you can also see between the pics. The engines output is 108 hp and the max. rpm is 2,600. Top speed was 150 km/h and the weight 1,055 kg.
Desmo or not? One citation in Auto-Revue 3.01.1958 : “Strange enough the first racers with such (desmo) valvegear date from 1914; It was a GP Delage and a Nagant.
Type of system still unknown.
Source colour picture: Racing Cars and record breakers 1898-1921 by T.R. Nicholson
nagantdoc1 nagantdoc2

Source: “Nagant” par Jacques et Yvette Kupélian In: Le fanatique de l’automobile; no. 89 (Febr. 1976). Translated [engine(head)information only] :
The engine was a four cilinder (94,5 x 158), of 4.4 liter, with 4 valves per cilinder and two OHC camshafts (Classic Twin-cam Engine).
In this very article there is unfortunately no mention of (semi)desmodromic valve actuation!
nagant1Nagant 1914 Belgium. Water cooled four vertical cylinders 94.5 x 158 mm 4433 cc.
Overhead 4-valver operated by two overhead cams. High-tension magneto ignition.
Five forward speeds, shaft drive.