I just checked the haynes manuals for you
the laggy1 has a speedo cable from the back corner of the gearbox(middle of engine bay) the cable curves up and across the back of the engine bay and passes through the firewall into the back of the speedo area.
If you have ABS it will also take a signal from the drivers side front wheel sensor.
(i am really not sure if there is a purely electronic only dash, (i havnt really stripped down too many lagunas other than the same ones as i own (standard RT without full electric taking dashboard).
There does appear to be 2 types of dashboard clocks, sagem and jaeger,
Note of warning, if you do remove the clocks from the dash, they MUST be kept upright at all times, as they have a reseviour of silicon inside the dials to keep them damped.
(which would explain why my clocks are so jumpy and are no longer damped - i must have lain them down on thier back at some time when i had them out a couple of years ago
, that'll teach me for not reading the manual properly!, never could understand why they suddenly got twitchy)
now the Laggy2 has fully electronic clocks/dashboard and takes its speedo readings from the ABS sensor on the front wheels.
same caution on handling the speedo assy if removed from the dashboard.
hope this info helps