How long (ballpark) can you workably make the gap between two flanged wheels?

I was looking at a small 4-4-0 earlier and thinking about perhaps not making the front bogie swivel, and instead just going with flanges for the rear driver and the lead bogie axle. Obviously, a lot of European rolling stock of modest size runs just fine on two axles, and I cannot imagine that this tiny locomotive is longer than, say, a turn-of-the-century UK passenger coach. Still, I figured I should ask. Has anyone toyed with this - running two widely-spaced flanged axles through switches...