Indeed, Roy Johnston's Timken "4 Aces" did possess a multiple-valve front-end poppet-valve throttle, however, it was upstream of the superheater, rather than downstream, as it would be on the prototype. Also, Roy's throttle had four different sizes of poppet valves, whereas the prototype had only two sizes of valves, at least that is my understanding, the pilot valve, and the main valves.
The same holds true for LBSC's poppet-valve throttle for his 3 1/2 inch gauge Britannia, at least the fact that it is upstream of the superheaters. I have, however, learned a great deal from both Roy's design and LBSC's design, but if I were to take design cues from them, their designs would require substantial modification to work in my locomotive, as Roys throttle is for a 4-8-4, and LBSC's design is for a 4-6-2, and neither design would fit in the smokebox of the G5s 4-6-0 I'm building: Roy's throttle of course is way too long and wide, and LBSC's is too small as it has only two valves, the pilot and main valve, where I would use no fewer than four main valves for a G5s, but that's just me.
P.S.: What, if any, benefits are there in having more main valves in the throttle?