The vent tubes are venting the bowl, and they are part of the carburetor casting. They cannot be separated or moved from the casting.
To install the carb with the bowl facing the back of the engine/firewall you will need to unbolt the carb (4-12mm or 13mm bolts) turn the carb 180-degrees, and then bolt it back down again. You might also need to replace the choke coolant hoses and adjust the other items hooked to the carb.
Depending on your skill level, this can be somewhat easy to somewhat difficult. Good luck!