I have had 2 Syncro driveshafts rebuilt by a driveline shop near me.
They do not use shims. They order the correct U-joints from a supplier.
The cost to replace both joints, balance, and paint the shaft is about
$175 if I  remember correctly. The only reason to use shims is to enable
the use of less expensive joints. The correct joints are available and I
even bought an extra one from them to carry on my Baja Syncro
adventures. The company is: Oceanside Driveline, (760)439-9718.
Mark Drillock