The problem with fitting liners that thick is that the barrel is very thin near the base flange and is very likely
to crack. Effectively the barrels have been bored about +0.200 Those liners are way too thick in my opinion.
You could have a few thou skimmed off the surface to true it up but if the liners are moving then more radical
measures need to be taken like drilling the base flange and putting pins or bolts in. Through bolting should also
be thought about as you've very little metal left on the barrel for strength.
I've had several sets of liners done over the years and never used stepped ones, if they are fitted properly
plain liners in iron barrels are fine. In alley barrels a step is nicer but that's if there is room.
Easier to find another set, they are cheap enough.