Dash frames are all the same. Standard clusters are the same physically, but the fonts are different for the 70 cars. Yours look correct for 73, but you have two lenses missing (high beam, oil?).
The cluster should mount to the tabs you are pointing to with four #10 phillips-head screws. They don't always line up perfectly.
The pad you have should accept a cap and fit on your frame with no issues. Again. the holes don't always line up well, so you'll need some wiggling and probably a few swear words to get them together.
Once you get that nasty gash straightened, the only problem I could forsee would be missing holes for the plastic trim pieces. 70 Challenger trim is different from all others, so watch for that. 70J parts have "pointed" edges.
Can you get a "straight-on" picture of where the gauges mount??
Steve