When I did the plane for this thread I had no cross marks either, but it's easy to work around.

Cut a sheet of plain white paper to fit the face of the firewall. Now you have something to mark on. I don't have a template and have since passed the plane along to someone else but perhaps a Sukhoi owner reading this thread will provide the off set from center for you.

Regretfully I'm forced to agree with n57tc. I too believe you're into a plane that appears to be well beyond your ability. Truly you need to find someone near you with a lot more experience to get you through the parts assembly and assist with the first flights.