I changed the switch on my 93, bought the tool from Boston Volvo, shipped it to WI and seems it was less than $50. Any way, basically you are trying to align the stud from the transmission to the scribed mark on the switch.( Black Painted area with scribe mark) It has been a few years since I changed mine, but a person could clamp two metal straight edges on each side of the stud flats with a very small clamp. This would give you a 3/16" "zone" to eye up the witness mark on the PNP switch with. A good set of eyes should be able to park the mark on the switch in between the two staight edges coming off the shaft. Basically that is what the fancy tool does from Volvo. I still have mine sitting on the shelf for future use.

Once the switch is in place, clamp it down and call it good. I would have done it that way if I had know what I was trying to acheive the first time, I just bought the tool because I figured I would be doing this fairly frequently. First two failed under warranty with less than 30,000 miles. Changed one at around 45,000 myself and I have 90,000 on the car now with no PNP trouble. 93 850 AT original owner