I'm pretty confident I can fill most the cracks... But one of the previous owners glued on a cover and there's a lot of rubber style glue everywhere

There's one on FB marketplace in Indiana for $100 that looks to be in a little better shape in my opinion. It's out of a '77.

That rubber glue may be the least of your problems!

I've done a Z dash pad restoration, starting with something that had only 25% of the deterioration that yours has. Even at that, it was a time-consuming job. Not only does the pad surface need to be levelled (not easy to get right, given the multiple contours), it's also necessary to 'V' and then feather-edge all of the cracks so that the filler won't crack along the seams. I'll bet it would take you 20 man-hours of effort (or more) to level, edge-treat, fill, sand, and paint a dash pad like yours to a decent level of final finish.

But before you even get started down that road, you'll need to convince yourself that what's left of your original pad has enough structural integrity to prevent the pieces from moving around independently when the cabin temperature goes up or down. With its many full-depth cracks, I don't think I would trust your badly broken-up dash pad to meet that requirement. As a litmus test, it would be interesting to know whether a professional dash restorer like Just Dashes would accept your dash for restoration. Maybe you should send a picture and ask them.

IMO, your best path forward will be to either: 1) buy a used dash that offers a better starting point for a DIY restoration (as Siteunseen suggests), or; 2) buy one of the replacement dash pads that have recently become available. In the latter case, you unbolt the old pad from the underlying steel structure (known as the 'armature') and then bolt on the replacement pad. There are a couple of threads on this site that discuss these replacement pads. As a third, lowest-cost/effort alternative, you could just replace your old plastic dash cap with a new one.