this is an interesting 89 Volvo 740 - it has the 16 valve head which I think makes it an interference motor
it has a steady miss like as if one of the spark plugs isn't working
all spark plugs - injectors - coil - distributor cap have been changed out and timing belt was replaced about 20K ago
compression is 120 to 130 psi - has lower mileage reading of 127,968

but what might be missing as to check and actually tell what is causing miss?

 

Take a compression test, may be you got a bad valve or a head gasket issue.

 

You didn't mention if you replaced the wires. I would just take an inductive timing light and put the inductive pick up on the sparkplug wire that has the miss. See what you get .

 

or spritz the wires with some water mist, then start the engine (hood open) in a dark garage to look for any arcing...