Hot Rods Harman Collins Mag - What's this extra drive for?

I've got this Harman Collins mag Model 8R101. Bought it some 10 years ago but never used it. Took out the box the other day.
As you can see from the pics it has an extra drive shaft with it additional to the crab style Flattie stuff.

Anyone know what this optional drive is for?
8BA or some OHV engine mabe? I rember seeing in some old pics of guys using these mags on OHV engines in early dragsters.

Any info appreciated.

Paul

 

What I see and I'm no expert.

Shaft for 49 to 54 Flathead,

Body and Electronics

Mounting base for either pre 49 and/or for setting up your mag as in a distributor set up tool.

Just guessing, others will be more knowledgeable than I.

 

Yeas the mounting base is for pre 49 Flathead.
Looks like a base usable for both 2 and 3 bolt covers.

 

Rotation would be backward for early ignition, but many flathead-mount style HC mags were built for reverse rotation use on front drives on OHV engines with timing chains. Went on aluminum front covers like a Hilborn drive would.

 

Hello Paul. Yes the shaft looks like a -49-53 size but they make them to
many others to. They are very nice this magnets , what i know they only have fixed timing but produce a great sparcle on the plugs. I have read are this a early magnet with this tag ,maybe -49 to-51 or--52 production . Too nice to have in a box,i have mine so i can see it everyday .