Is this old steel frame MTB too big based on standover clearance?
If the bike is comfortable to ride for you, then it is a good size for you.  While standover room is important, you might choose to lean the bike more when stopping, in order to reach the ground.
One option is to fit some slick 26&quot; tyres to gain some extra tolerance for the bearings  - you'll want to do that anyway.  Something like the &quot;continental Grand Prix 26 inch&quot; is 1+1/8&quot; and has a road biased design.   Compared to a 2&quot; tyre you'll drop the frame about 35-40mm.   Do consider pedal strike on the road though.