Just put one of these in my primo condition '66 Vibra-Champ.
http://store.yahoo.com/triodeel/tfchxfwi48oh.html
Didn't have to drill any holes. I covered the 8 ohm tap wires with heat shink and routed them out between the cabinet and chassis.
Used one of those bullet shaped female Switchcraft external jacks.
It jst dangles right below the 4 ohm RCA connector.
I use an 8 ohm Celestion 12 in an extension cab and it sounds great!
You can also run the amp's speaker and the extension at the same time.
Not bad for under $20 and 30 minutes work.
