7.25 to 8.75 conversion 1974 Valiant

No, you can't use the '74 drums for your application.
Since you've got redrilled A body axles, you have two choices:
1.) Find some small bolt pattern 10" drums AND BACKING PLATES, have them redrilled to 4.5" B.C. to match your redrilled axles. Use '72 and earlier brake hardware ('69-'72 preferred). New drum availability is spotty, at best, and not cheap when you do find them. MUST be paired with the correct backing plates (NOT interchangeable with ANY others).
2.) Get aftermarket axles with the 4.5" bolt circle. Doctor Diff has them for under $300 with new bearings installed. Mopar Axle Package 5 X 4 1/2" (5 X 4.5) Bolt Pattern 30/35 Spline Now you can use your '74 drums and backing plates.
Why can't I use my drums, you ask? Because the A body (4" bolt circle) flange offset (do a forum search on it, lots of threads explaining it) is different from the 4.5 axles. Plus, the center register on your axles is substantially smaller than the center register on your '74 drums... wobble wobble wobble.