What were the differences in dash speakers?

It really depends upon a few variables. In our case, my son's car was completely dismantled for a total rebuild. That made it much easier for us, because nothing was in the way, such as the A/C-heater box and controls.
We simply reached up from the bottom, before all the "stuff" went in.

My guess is if you remove the glove box insert, it will give you better access.
If you can remove the defrost hoses, it should really be opened up quite a bit
under the dash. No A/C would be even better. Honestly, it's basically what you would have to do to gain access to replace the nylon pivots when your wiper linkage arms are slapping around under the dash.

Sound fun or what?
Jerry