I never thought about going in through the speaker hole.

Push the driver's seat all the way back, lay on the floor under the steering wheel collum and remove the insulation pad that covers up the wiring and such so you can see up under the dash area.

Reach up slowly and carefully behind the instrument panel and feel for some knurled knobs that hold the instrument pod to the dash board. These knobs are just like the ones that hold the taillights in if you need to know what you are feeling for.

I seem to recall that there are three of these knobs that will need to be removed, but you never know. After all these years and previous owners one, two or perhaps all three of the knobs could be missing. The instruments will stay in the dash with no knobs at all, so they may all be missing.

Once all the knobs are off you can push the instrument cluster out from behind. It is only held in by the friction of a rubber "band" that goes around it and the wriing and the speedo cable that is attached to it plus the instrument pod. There is ususally enough slack in these lines that you can pull them it out far enough to undo them.

CAUTION::::: The water temp and the oil pressure on the 108 are not gauges; they are instruments. It has been about ten years since I have pulled one of these, but I recall having to take some special care when removing this part of the cluster.