This is what is says in the FAQs

[SGFM] "Relays in most cars pull straight up from the relay base. However, in some 760 models (with relays located behind the lower dash panel below the stereo, facing the passenger side) the relays have retention devices. Two sides of each relay are held by plastic clips that must be pried OUTWARD at the same time to allow removal of the relays. Unless you accomplish this maneuver, you'll either break the relay or the retention device when forcing the relay out. I found that toothpicks wedged into each side retention device allowed the relay to be removed with the least amount of pain. In the 760/960 diagram shown above, A, B, F, J, L, and M are permanently attached to the board."

In both my 89 760 and my 88 760 all of the relays are removeable. It is true that some of the sockets are not removeable. The black tabs hold the sockets in place, not the relays. In my car for sure, I can't speak for all models but I can not imgine manufafcturing/moulding a base with built in relays.

--
88 765 w/2stage boost (TO.)