I converted a tricycle landing gear to a tail dragger. How do I now determing the CG?
Thanks,
Laurence

cg is the same placement of the landing gear has nothing to do with the cg location.

Just to clarify what aerowoof has said. Your CG location needs to be the same as it was prior to the modification. Moving your gear certainly can change your CG and it should be checked prior to flying. Also if you did not already figure it out the main gear now needs to be in front of that CG to avoid nose overs. Putting the wheels in-line with the wings leading edge seems to be a good place for most.

A 20 degree angle between the axle and the CG is another good starting point.