Carlos is (as is mostly usual) pretty much on the money. The ZNDF started off with L1 SLRs, Sterlings, GPMGs... the full British Commonwealth standard for the time in fact, including 2" mortars. During the '70s they became the conduit through which Soviet equipment was passed to ZIPRA and other Freedom Fighters within Zambia. At this point AKs began appearing in the ranks of the three regular battalions, with the British kit (along with Enfields, Brens and Stens) appearing when the army was occasionally expanded to its full 9 battalions following some emergency or public demand for action against Rhodesian incursions.
Occasional raids by the aforementioned freedom fighters on the various Zambian paramilitary camps (Police reserve etc.) Further reduced the stocks of British items, which were made good from Soviet aid.
With the exception of the aforementioned Ferrets, the ZNDF was transported by truck and Landrover/UAZ. It wasn't until the '80s that Soviet armoured vehicles entered the inventory. For reasons best known to himself, Kaunda would not build up his military with heavy gear other than AA weapons and even the ZIPRA 'mechanised' force was stored in Angola, with other items smuggled into Zambia and then being buried to avoid upsetting him.
There's a useful chapter here:
http://www.issafrica.org/pubs/Books/Evol_Revol%20Oct%2005/Chap12.pdf but which gives little away as far as equipment goes for the '70s. Barring 81mm mortars, 37mm Bofors, Yugoslav M.50 triple 20mm and the OTO-Melara 105mm howitzers, everything else seems to have been acquired in the '80s.