I have an lt-40 that I am converting into a tail-dragger, how do I make sure the front gear is centerd and track straight? my fire wall has been replaced, so I can't really take my measurment from there.

Just get it close and tweak the gear if needed. It will only be perfect until your first bounced landing or long car ride anyway.

The AXLES of the LG should be even with the leading edge of the wing. You also want your wheels to have A LITTLE TOE IN.

You can use a "builders square" from the fuselage side. Do it from both sides if the sides are not parallel and average out the difference. This isn't as difficult as you are making it. Not really that critical.