single point dist setup - adjustable advance ?

[gtx6970]

Well after waiting and waiting with no forward progress - I decided to redo the igniton dist myself.

I've got the stock 2875758 single point dist scattered all over the bench - and have found out the original advance unit  is toast.

and so far, have been unable to locate a new one,
I've found and nos one for  1969 383 2 bbl and it looks the same as far as outward appearnce.

so my question is, are they adjustable to some degree or am I better off sticking to finding an original for the factory dist. ?