I fitted front speed sensitive parking sensors to our MK2. It is quite a bit more complicated if you want to go down the speed sensitive road. They cut in at around 6mph, anything above and they switch themselves off.
You can fit front ones with an on/off switch which would be easier but in my mind a bit of a fag.
Mine came from Dolphin back and front sets and with the magic box came to over a £150. The box of tricks if I remember cost circa £50 +. It is possible to find cheaper but I couldn't find a supplier for the speed sensitive gizmo on E bay. I am not sure about a MK 1 but I found afterwards that I did not need to remove the bumper could have done it through the hole after the grill was removed.
The two biggest problems were getting the wiring through from the engine compartment to the inside and also the connection needed to pick up the cables for the magic box. As it had to pick up two wires from the OBD 2 circuit, rather than cut into the loom I bought a male OBD 2 plug and just soldered the two wires into the relevant pins. I can just remove the plug if I want access to the OBD 2 socket. I can still switch the system off if required but touch wood they work very well EXCEPT in narrow lanes when they shout about coming close to a bank is a bit of a nuisance ( could be a benefit). If you are fairly competent around the car and want to try, just take your time and if you do go ahead and need it I will try and help