Not sure which dash you got so bear with me. If you got any pictures of the back of the dash you bought and some of your current dashboard then that'll help, the new one may have been fettled with by the last owner, did you get any brackets with this one?
Is this the cradle you mean? If so then yes it needs to come out, access to the bolts are in the engine bay on the bulkhead, your speedo cluster will need to be screwed into your dash direct, don't use screws that are too long though


Your new dash should have these fittings, three of them, left right and center

These are the brackets that are held in place by the top/bottom of the dashrail, last owner may have kept these for his new dash, though you get these with new ones anyway.

The top sections of the brackets point towards you so therefore they sit in the dashrails so the dash is then secured with the wing nuts.
If you aint got these then you could make some up, not difficult but dont use anything light as when you tighten the wing nuts it'll just bend, but make sure you got the fittings on the dash first!
Hth