before they removed the old rubber bushing they marked from centre of bolt hole down 4 inches and marked it on the trailing arm, then they had a datum to work with when reassembling them, using the old bolt hole as a reference is no good if you didn't find a measurement before disassembly.
if all rear trailing arms are the same or similiar you could find out what that measurement is (from centre of bushing bolt hole to the hole in the trailing arm
and set them up to that, as he said you will need an alignment anyway so you will be able to get it close enough, hope that helps.