You don't have to sell the 80 but you do have to put some effort into getting the car seats mounted securely. I was able to safely mount rear and forward facing seats in our 80. Fortunately we have recently graduated to boosters.
For the rear facing seats, which are relatively easy to mount, I went with a 2 part setup where the base was permanently mounted to the car and the kid carrier snapped in and out of that base. The base was secured to the car seat using the seatbelt. An important trick that works in my '97 80 and in most newer cars is that when using the seatbelt securing method you want to fully extend the seatbelt (pull it all the way out) to engage the ratcheting function as it then retracts from full extension. This feature was added to seatbelts to support mounting car seats with the seat belt and allows you to snug the seat into place with the belt and not have the kid seat flopping around when mounted due to a loose seatbelt. Your 2nd and 3rd row seat belts should have this feature.
When we moved up to forward facing seats I found that the Evenflow Tribute car seats used metal hooks that are intended to connect to the latch system. I was able to use those metal hooks to connect the evenflow seats to the 80. On the inner side of the kid seat I used the hook around the loop on the short end of the seatbelt. The female end of the seatbelt has the webbing looped and stitched over the socket/receptacle for the seatbelt and you can use the metal hook from the car seat to connect to the webbing loop on the inside edge of the kid seat, which is very secure. On the outer edge of the seat I would mount the metal hook over the bottom hinge plate. The third, top strap goes under the headrest and down to the floor anchor in the rear cargo area behind the 2nd row seat.
I should point out that with the evenflow seat metal hooks you have to put the metal hook in the correct place on the 80's seat hinge plate so that it doesn't slip off. You also need to orient the strap in the correct direction so that you can pull the tensioner and get the seat really tightly mounted. I would use my body weight to push the kid seat down into the cushion of the car/80 seat while I pulled the slack out of the lower retaining strap. Once the lower strap was tight I would add the third strap over the seat back, to the floor, and just snug it up but not make the 3rd strap too tight. From there you wiggle/shake the seat around and see if it loosens up, then repeat until it stays secure even with pulling/pushing on the seat. If you pull too tightly on the 3rd strap then you tilt the seat back and push your kids feet forward. This doesn't matter as much when they are small but is more relevant when they are taller.
When needed I was able to mount the same forward facing car seats in the 3rd row using the same techniques (seatbelt loop inside, hinge plate outside, cargo hook behind seat).
I used a seat protector under the car seats. It helps a lot with cleaning up the mess and also will help prevent deforming the leather at the contact points from the car seat.
Most of us 80s are gear heads and you can apply similar skills/attention to keeping the kid car seats setup correctly. Shoulder strap positioning, cushion adjustments, etc. can make a big difference in kid comfort while traveling and when they are young they can't tell you if things are off, they just cry. You have to figure it all out for them as part of the efforts to travel as peacefully and safely as possible.
Good luck!
