I have two of these horns also. Are you sure the capacitors are bad? Unless the capacitors are corroded bad, I bet they are ok.
You can check to see if they charge up with an ohmmeter. My horns have the same capacitors in them, they aren't marked with a farad amount. They are about an inch long and and a little over half inch in diameter, and mount into a neat little bracket assembly. Replacing them with something else would be possible, but it would be a lot easier with the right size. There is a set if points in there, if they are corroded it won't work. The adjustment is touchy, too.
Jim S.

Phil;

To expand on what George has said, I'd install an ignition capacitor if you can find the room in there...without a cap, the contacts would not last very long...

Cheers

All the capacitor does is reduce arcing at the points, just like the ignition capacitor.
Therefore exact value is noncritical. Whatever you got should work OK.
In fact it will work without but won't last as long.
--
George Downs Bartlesville, Oklahoma