I've done much the same on my Princess of Wales cylinder block. The centre looked like swiss cheese when I bored it to 1.5", I couldn't return it as Reeves had changed hands by the time I found out, so I bored out further to 1 5/8", about the maximum that I dared, and fitted PB liners of 1 3/8" bore. I went for the 1/8" wall thickness to keep the liners fairly sturdy for pressing in, (no dry ice!), the end covers also help retain them and it looks OK, though I've not completed the loco yet. My guess is that the reduced bore won't be too noticeable. As a single-wheeler, PoW will never be a load hauler!

BTW, isn't your area reduction ~20%?

Food for thought. I am having very early thoughts about "what next" The cylinders are at the forefront. I am thinking in terms of inside cylinders machined from steel and then lined. Theory is that the ports (slide valves) can be cut right through to the bore, hence steam passages can be parrallel to the bore. The press fit/locctite liner then sealing the ends of the ports. My current plan is a cast iron liner with 3mm wall thickness. But the earlier post here suggests PB. What do you all think.

Regards, Bruno.