It is the holy grail for pure classic/hard rock, if you have one of the two following:
an actual 67-73 1959 that hasn't been modded,
or a modern 1959 amp that has been built or modified to replicate it exactly
You can get that sound out of a 1959slp reissue, but only with quite a bit of changes - the Output Transformers (heart of the amp) are cr@p and need changing, and it'll need decent tubes and be running through the right speakers.
Something like a DSL might be able to produce plexi like tones, but it'd never be able to get that 'magic' that a decent 1959 would. There's so much going on in those circuits that they end up being "jack of all trades, master of none", even when the power tubes are maxed out. The key to that coveted "plexi sound" is the pure signal path with a decent OT and tubes.