Twin Pegasus (by Bristol): makes sense?

Let's say Bristol develops the 18 cylinder radial engine, based upon the Pegasus. The development is at back burner prior the ww2 breaks out, as an insurance against possible issues with sleeve valve technology. Any uses for that? 1800-2000 HP should be within scope, too tempting to pass on the opportunity to have it installed? With the benefit of hindsight, how easy/hard would it be for Bristol to pull it off?

Boy, talk about a can of worms?

It might have gone very smoothly, on the other hand the the R-3350 was either an R-2600 with two more Cylinders per row or two R-1820s with a shorter stroke put together, depending on how you look at it. We know how long that took to sort out

Also look up the Alfa 135 aircraft engine which is the Italian version of what you are talking about.

Bristol didn't have capacity to develop this engine and the sleeve valves at the same time, especially as Roy Fedden (chief designer) didn't think he could design a suitable arrangement for driving the valve train on the rear cylinders which is one of the reasons he went to sleeve valves.
Very little work was done on the poppet valve engines once they started on the sleeve valves. Just enough to rate them on 100 octane without any real attempt to exploit the 100 octane.