I think your best bet is to get the correct 5 pin switches. I'm not certain on this but I think the 3 pins were for 4 door cars that had a relay in the system.
So, if I'm thinking about this correctly the 3 terminal switch and plug has a feed wire, lock wire and unlock wire.
Going by the wiring diagram, the 5 terminal 2nd gen F body switches come in 2 flavors for the right and left side. For the sake of conversation, let's say that the plug for switch A will have a feed wire, 2 wires to lock right and left side and 2 wires to unlock left and right. The second switch, call it switch B, has a plug with one feed wire, one wire to lock right and left side, one wire to unlock right and left side and 2 wires for ground. Orange is the power feed, black is lock, light blue is unlock and black with white stripe are grounds. I'm assuming that grounds for both sides are handled by switch B.
To make the 3 terminal switch work all you should have to do is connect the 2 same colored wires together on switch A and connect them to there respective terminals. The problem as I see it are the 2 grounds on switch B; I have no idea on what to do with those and without them the system will not work. To the best of my shade-tree knowledge you would need to do a relay upgrade in order to make the 3 terminal switches work.
