The tuner appears to not have an understanding how and why vacuum advance is applied.
Hook it up to ported vacuum source and go for a drive. On a level road or slight uphill, constant pedal, does it surge or ping? If not, leave it hooked up.
A low compression, stock shortblock 318 can likely take all of that 51* of timing at cruise. Especially true if it is a post 72 model shortblock.