Originally Posted by Brett Blackmore
Super Basses and Super Leads supposedly were largely the same (as was the Super PA), and at the time many Marshalls were one-offs – basically the same, but different components here and there.
The early incarnations were quite close, but by 1968 the circuits were less similar. The split (rather than shared) cathode of the later superleads was quite a bit more gainy and aggressive, and through the years the Superleads became brighter and brighter. All the re-issues (other than the JTM45-100) have split cathode also, and most have later 70's style circuitry rather than the classic sounding amps. Even the handwired SLP isn't really very authentic.
Back to the OP;
As for a class 5 being close, well I wouldn't bank on it, but you can always try.