Who made the drivers for the Mission 770?

And...what would be for a fair price to pay for Mission 770 speakers (c.1978) that have had the midbass units replaced with OE drivers? What other concerns (besides driver deterioration) might one have when purchasing 20+ year old speakers? Crossovers? Wiring? Cosmetics are of minimal importance to me. Thanks!
the mid/bass unit is designed by mission while the tweeter is seas

I am still using a pair of 770 but i have changed the tweeters and replaced internal crossover capacitors with the same value metalized polyproplene caps
Just looked at one of my old-(blown) mission 770 drivers.
They are made by SEAS in Scandinavia. the model # is
214/MPDD with patented dynamic damping* motor system

*No: 138 504