Does it matter if the fuel tank is mounted front to back or left to right. I am removing 1.5"-2" of my firewall back to a more scale position. Problem is I am running out of room up front and would like to mount the tank sideways to make more room.

No, other than you may suck air and konk out doing knife-edge if the klunk is above the "waterline" for too long.

Be sure to balance as normal and then re-balance with a full tank to make sure you don't become tail heavy when fueled up. Otherwise your first flight may be short and crunchy.