I have used the 4.5 regulator on 3.5 before for test purposes. As I said above they are different. The one on a Volvo or VW from around 1971 might be closer. The 4.5 doesn't have the full load stop built into the regulator as the full throttle enrichment is handled electronically with a full throttle position on the throttle switch.
The 164E volvo that you need would be the earliest ones with EFI (probably 1971-1973. The latest ones didn't have ignition points if I recall correctly.
Bosch Master, ASE Master, L1
33 years MB technician