dist lengths: SB-3&7/8. low deck-3.5" RB/hemi-4". I cant see the dist with the OE light spring/heavy spring with elongated loop on one end combo being full advanced that early. EDIT found my chart

I've been through that lesson, the small block distributor or a BB distributor in the wrong motor will retard the timing as you rev it up
They have opposite rotation of each other

So I take apart one distributor and put in two stock medium thickness springs and everything is working fine. Initial timing set at 12 degrees and advances to 34 at 2200rpm. Did not take it out on the road yet, but now I can rework the slots in the advance mechinism if I need more initial timing. Finally going in the right direction.

A BB and SB dist dont turn the same direction so they dont fit(gear
turns opposite

One of the SB stock distributers will slide in and start up in BB but it will retard the timing as you rev it up, when in doubt make sure you have the correct part for your motor
I think the main distributer shaft in the SB may be around .04 to .100 longer than the proper distributor shaft but it will fit and run

Cab.. do they both turn the same direction.. thanks

No, one (SB) is clockwise and the other BB is counter clockwise, the motor know when it gets the spark near TDC that the plug will fire and start and run, as you rev it up the distributor will retard the timing instead of advancing it
It fits, it runs but not good