91 YJ should be front disc rear drums with 3.43 (or something in that order) gears.

The 8.8 is a good swap with limited spring perch work needed.

Personally, I would go with 4.56 gears; but that is your choice and the 4.88s will work. You will have a little higher highway rpm.

Drum to disc is a fairly straight forward conversion. However, there are issues depending on the axle. D44 has 3 different bearing retainer plates. One is specific for disc brake installs.

Not sure about 8.8.

Overall, the D30 front and 8.8 rear are a good combination for trails rigs looking to maintain a balance between highway and trail performance.