I''m thinking the same as Bill's suggestion; assuming that you are
using omni antennas (makes sense here), set up your routers not at the
very ends but in the barbell shape, maybe with a third in the middle.

Considering that you are trying to cover a long area, you may want to
go ahead and keep the 2-wire radio operating as well.

Placement is going to be everything. Luckily, your area is only 30 ft
wide, so it will be a line, not a grid. Try to set up so there is
always an AP within 2 walls of any user.

Here's a suggestion:
Make a map of the walls and the needed coverage to play around with
locations for the APs.
Place one AP two walls in from the end of your desired coverage. Go
four walls over and place the middle router. Go four walls further
and place the end router. Hopefully you have now covered the whole
thing. Make sure that your middle router is on a different channel
than your end ones at least.

Who knows if it will ever work with all the other APs that seem to be
present. I would do a site survey first to see what the channel
mapping currently is. You might be able to prevail upon one or two
key AP owners to switch channels so that everything works better.
Failing any of that, doing it blindly, I would assume that most are
set to channel 6 and that using 1 and 11 for your APs will help.