Blanik L-13 Weight and Balance

We need to get a weight and balance done for our Blanik L-13. The
manuals are not really helpful referring to percentage of MAC (mean
aerodynamic chord) for the CG range without saying how much MAC is
nor where the reference plane/datum is (probably the wing root rib).

I dug up the FAA type certificate that actually uses the "most forward
point on fuselage nose" as the datum and specifies the arm for front
and back pilot plus the C/G range relative to that datum which should
give me all the info needed to do the calculations for minimum single
pilot weight etc. Only problem is that the FAA type certificate states
that the leveling means for weighing the glider are "between points
marked on side of fuselage". Now that is not very helpful either since
ours has been painted several times and the manual doesn't make you
any wiser either as to where those points are.

Does anyone out there know how to establish the proper leveling of the
Blanik L-13 when weighing it or has a better method for doing the
weight and balance for that glider?

Thanks in advance for any help you can provide,

Markus Graeber
Aeroclub de Colombia