Yes, the PA18 was certified with the C90-12 or -8. _8 being no electrical system. From the Typer Certificate Data Sheet:
Engine Models PA-18 and PA-19:
Continental C-90-12F or C-90-8F (Uses carburetor setting No. 530726)
(See Item 106 for Models PA-18 "125" and PA-18A, Item 108 for Models PA-18 "135" and PA-18A "135", and NOTE 3 for Model PA-18 "105" (Special))
(See also Items 101, 106 and 108 for optional engines)
Well, actually you can go as far under class B airspace as you wish, as long as you don't enter class B. 91.215(3). But if the airplane was certified with it, you can't just remove it. It does specify "engine-driven" electrical system so it is possible to have a starter with a battery, you just can't have an alternator attached to it too.
I've been looking for a -95 without the electrical system. The estate one I'm looking at has a starter button, which means it is probably a -12 engine.
my PA18 L18C Supercub C90 - 8 is certified and has no electrics. Use a hand held radio clipped on to the dash and wired into an intercom box (both rechargable units) and wired so that I can use Pilot and Pax headsets and PTT located on the Pilot stick and next to throttle in the Pax seat. You can view my aircraft on Trademe (NZ website) Its up for sale at the moment. Click on cars, bikes and boats and then click on 'other vehicles - aircraft.
Its the only cub for sale out of the 180 odd aircraft.
All of the original advertising literature mentions that "electrical system is optional". I do believe that the majority of the original customers ordered the electrical option as one seldom sees a non-electric PA-18.