The Q classes were all 2-8-2 Mikado engines

The P classes were all 4-6-2 Pacific engines.

An elementary, but interesting, British account of mechanical stoking in the early years of stoker design is here:

railwaywondersoftheworld.com/firing.html

One of the 'issues' in rear-feeding stokers has been the necessity of supplying a proper 'heel' at the back of the firebox (from which hot, but unburned coal can 'slide' down the inclined grates for even feed outside the turbulent flow of gas from the fire back under the arch). While an FD stoker could easily place coal 'with the flow' (as in throat-fired oil setups) it might also be relatively difficult to get coal precisely into the back corners without it becoming 'triturated' in the process, or erosive to the lower backhead area, or indeed get a rear heel hot-soaked to an excessive temperature.

The front corners of the firebox now become those that have to be fed from the special channels in the distributor plate that were supposed to do that job in, say, MB series stokers. I have to assume that the Standard Stoker development people carefully considered this and tested to ensure that the distribution there would not have the effect of building a heel at the front of the box... but only testing of an FD in an actual firebox might demonstrate how well the planning actually worked.

Yes, I'd like to see 'somebody' 'gin up one of these things, perhaps using preserved MB-series stoker parts and dimensioning to get close to the historical case (as with the T1 replication) and see how it behaved in simulated or actual road conditions. No, I wouldn't want to have to pay for it.

Is there any wau to tell from the B&O records how many, if any, of these were applied to locomotives with Emerson fireboxes?