A Volvo conversion Weber manifold should have two vacuum nipples on it for brake booster and crankcase vent. If it is a B18, I would suggest to convert to the B20 flame trap (or use the B230F conversion kit) and get rid of the PCV. The manifold nipple is a special one with a small hole in it. The large open bore nipple should be used for the brake booster.
If you decide to use the B230F flame trap conversion kit, then you can use a port on the intake side (before the carb, placed in the air cleaner) skip the nipple on the manifold and add a small vacuum line to the carb base to the flame trap holder, which should be there on a 32/36 DGV Weber.
This is the best performance way to add a crankcase breather to the old B18/20 motors. I convert all my B20 builds this way.