Hello Iking,
don't have either kit but going off the top of my head as I'm currently building (or reconstructing) a DML BTR-70:
Turret-in 1984a second turret roof periscope was added. In 1986 a vision block was added to the left turret side and the last model mounts a BTR-80 turret, minus the smoke dischargers on the back.
Headlight guards- late model uses -80 sheet metal guards while early uses tubular guards.
swim vane-late mounts a swim vane very similar to -80 in addition to small buffers on the hull nose to protect the vane mounting tubes from damage. The early version lacks these as the tubes run around the hull side rather than the nose.
late model has gun ports on the angled portions of the roof.
Wheels seem to be completely interchangeable between -70 and -80 so you might see a mixture of all of them even on the same vehicle.
I recently picked up the Trumpeter -80 kit in order to cast some of the parts for my -70 project and if it's anything like the -70 kits you won't be disappointed ! Let me know if you need any references.

Sean