only thing you may want to look into is the size and location of the marker lights on the quarters and fenders.
the 70/71 stripe kit might assume 70/71 marker lights and the wholes located in a specific place.
FWIW ..
I got my stripe kit for my 70 from David Patik at Performance Car Graphics.
You may want to give him a call and see if there are differences you need to address.
on a 70 challenger the side stripe goes above the side markers lights. i beleave the location on a 72-74 is the same but the shape is different. i do agree that it is better to ask the company that sells them, but then agane you could trim them to fit if needed.
thinking of using Phoenix Graphix ..do you need the stuff they sell to aid in putting these on or is there something else that works ..haven't done any this large like the hood blackout
70 & 71 RT stripes will fit. Early and late side marker lights are in a different position and make no difference on the stripe. The large hood blackout can be fun to do. I would use what Phoenix sells because it is compatable with their decal material. I don't know who supplied their material.