Schematics here http://fa.utfs.org/diy/roland100/
. I've been peering at the System 700 schematics for the last few weeks and the System 100 service manual is amazing in comparison.
For sync I'd suggest recreating the bit on board OP-29, page 12 - follow the hard and soft sync inputs to the caps C412 and C413. The output of that would go into point 42 on the VCO board. Here's the VCO board on mine, point 42 is in the middle - you might be need to be careful with routing the wire into it out of the way.