I do not think it would be a good idea to modify that distributor. Of course, just about anything can be imagineered into something else.
The mechanical tachometer drive I built for our Cummins 4bta is driven off the injection pump gear. The injection pump turns at 50% of the crankshaft speed as does the cam in most engines. The first concern for me is to check for front engine clearance for the drive and if necessary, possibly making a reroute for the drive belts that interfere with that space. A nice touch is to convert all of the pulleys to modern SERPINTINE belts and one tensioner. These belts lend themselves well to bending in both directions,
BUT, alignment is super critical.
I bought a SBC HEU distributor from a neighbour who was parting out his MALIBOU. A little time in the lathe and a new Ford Flathead distributor drive gear, from THE OLD CAR CENTRE, fitted had the HEI firing a different application. The HEI advance had to be restricted for the Flathead. This modification will have to be determined by the end-user.
To make a working mechanical drive will require some Stewart
Warnerhttp://www.stewart-warner.com/ or SS White
http://www.sswt.com/products.htm shafts and most likely an angle drive will be needed to turn the drive to the cable 90 degrees. These drives can be opened and the out-put direction reversed.
The second option may be to try and find a distributor from another engine that has the mechanical tach drive. Another tachometer option may be one that had a governor drive connection. This may be an easy conversion to a drive cable. Some of the governors were driven by a speedo style cable.
I am going to call my friend about the IHC tach drive distributor that I gave him, maybe he still has it and maybe he will let me get it back. If I am able to get the distributor, it will be a good source for what to look for.
I saw an IHC stationary engine near CHILLIWACK, BC, and it had a tach drive distributor and the engine drove a large gen-set for a chicken barn emergency power.