K Frame is the same. All V8's except the Hemi had the same basic Kframe.
Motor Mount isolators are the same, (Rubber part)
Motor Mount Brackets (Metal bracket on engine to Rubber isolator) are different.
Transmission mount and isolator are the same.

1970 floor shift cars had a shift interlock linkage. It is not needed if you lock the shift tube in the column and it is a floor shift car. If you keep it, then it will be different big block to small block and 904 to 727

If the transmission is already a 727 floor shift then New transmission and kickdown linkage are needed but all else is the same.

If the transmission is a floor shift 904 then:
The bracket that holds the lower part of the shifter bellcrank is different,
The kickdown linkage is different
Probably the Rod to the shift lever.
Driveshaft and slip yoke are different too.
Of course you need the 727 Transmission.

Column shift cars need the correct bracket for the shift linkage for the Big Block. Nearly all linkage if swapping from 904 to 727. I doubt it is column shift. Not many column shift Challengers.

Rear end is OK if it is and 8-3/4, Gear change is optional.

Sway bar is a nice plus. Can be left off but really worth it in my opinion.

Torsion bars will need to be replaced and if you drive hard the rear springs will probably need to be looked at.

Exhaust is different and you would want duals instead of single anyway.

Engine wiring is slightly different. A new engine harness or modify the old one.

Power steering brackets and probably hoses.

If you have/want AC the brackets and hoses are different.

Radiator, fan shroud and hoses need replaced if it is still stock.

Not a hard job except finding or paying for the linkage.