I did the same on my 220. left the stock coil in there (possible back up) and used 2 coil mounting brackets to attach the new coil to the old coil (one around each and a bolt tying it together) Looks clean enough and keeps the new coil out of harms way. If you set it up right you will be very pleased,. The 75 ignition was the best thing I ever did to my B18. I've had it in 3 cars, your little black 2 dr looks good, had a black one as well, with all new bushings etc it was a very fun car to drive....not like my understeering 220.
--
Patrick ('68 220, '83 245).

I wired in the 1975 breakerless distributer into by 1967 Volvo 122S with no problem. I kept the original armored coil and the 123GT Smiths tach and followed the instructions found in the vclassic archives at;
http://vclassics.com/ archive/breakerless.htm
Hope this helps.

I haven't done it yet but one of these days (when I get a 122 running again) I plan to
try using the armored coil with the 75 distributor. It will require some different wiring
but I think it may work OK.

The armor wire carries 12V from the ignition switch to the coil; you'll have to come up with a switched 12V source for the new coil.

You can leave the armored cable hooked up -- just remove the visible connections from the stock coil.