I've upgraded a Type 9 Stanley #3 with a PMV-11 blade and had to file the opening to fit the thicker blade. I took my time filing, and all of a sudden the plane started to perform admirably. I can just fit a 0.01" feeler gauge between the blade and front sole; the blade is supported BOTH by the sole and the frog, and can take of a (to me) unbelievably thin full-width shaving in the trickiest of woods. (I've cleaned up and kept the original chipbreaker.)
The problem is that I have no adjustment capability, and the blade is only good for ~3 honings before I have to rebuild the primary bevel.
My question is whether to keep going (with filing the mouth) or accept this as a special-purpose non-adjustable plane from now on. It would be awesome if I could retain this level of performance with a degree of blade adjustability, but it performs so much better than my #4 LV, that I wonder if it's realistic to expect it to work as well if I keep filing the mouth.