Will this work with an 8 1/4?

Is the 7 1/4 a bbp or small bolt pattern.

We just swapped a complete BBP brake set up off a 7 1/4 right onto an 8.75. An 8.25 will use the same stuff. The one thing you may need to do is drill the 5th hole in your backing plate going from 7.25 to 8.25. Some 7.25's only have 4 axle flange stud/nuts.

If it's a small bolt pattern, then it won't work.