Here's a list of mods that I'd do if someone were to give me one of the 90-size eindecker kits:

1. Replace the slab fuselage walls with 1/4" balsa structure from the wing area back.
2. Go with a full-flying rudder and tail plane
3. Make up a "sprung" tail skid (a must for hard landings)
4. Solder a slightly more scale-looking UC out of music wire.
5. Build a recessed firewall to allow a scale depth cowl (metal pot if possible).
6. Pull-pull on both rudder and tail plane.

The rest I might just leave the way is it an enjoy it as a nice fun-scale flyer.