Hi Rich and thank you,
I was concerned that the sleepers available for P4 would be a bit too short for a 21 mm track gauge, but for a 8ft 6'' length a 32mm length sleeper should be OK, however I presumed that prior the 60's the sleepers used would have been a bit longer. I think that the P4 std length is 34 mm (?) for a sleeper so they should be Ok.
I still have a lot to consider but I will certainly move to P4 for my irish modelling in a mid term. I do not like the look of the "of the shelf" OO track anymore. I believe that a hand build track will look much better and it is doable. So if I start build my track I may as well model at 21mm. The conversion of the rolling stock is the biggest concern though.
Luc