Of course you can, and this is what most people do since the primary dimension is usually the seat-tube length. You can always get a longer or shorter stem to adjust for reach. You can also get seat-posts with varying amounts of set back or none at all to further fine tune reach. 'Stand-over' is a bike dimension. Riders do not have stand-over, they have 'inseam' and done properly inseam is measured barefoot, but when riding it will likely be in shoes of some kind. My vintage road racer is impossible to straddle barefoot, but it is quite easy to do so in cycling shoes. It's a very big frame but I still need about 4.5" of seatpost showing. If I wanted to make a flat bar road bike out of it I would not go looking for a different frame with a longer top tube I would simply buy a longer stem. Around 20mm longer usually does the trick.