SBM Distributor overhaul DIY?

340's, even in '68, had little initial and then a quick primary advance.
Dodge and Plymouth used slightly different numbers but either way give it more initial and shorten the advance.
depending on how its built it will like a little more initial or a bunch. 10 to 12 initial minimum IMO. Start moving around 650 rpm if close to stock.
360 Tune Up