I was readin up on your arduin tach. I don't know much about optocouplers. Is there another part that would replace the H11LMS? I see some H11L without the MS. Is that just the form factor? 

My car is the silver one at this link"

http://www.datsunvents.com/dvimage/CustomerCars/Solex68%20(600%20x%20426).jpg

have a look at https://github.com/seanauff/classic-car-sensor-interface or https://github.com/seanauff/classic-car-sensor-interface/tree/teensy 

I was planning on doing that to my '57 chevy 210 but then I bought a house and am more IoT focused now

Nice , yeah I'am building a shop so this is going slow .... and on your 57 , Doit ! and post it up here ... I moved away from the teensy and I started on the mega for this project . Now I'm building a custom FPGA ... I'm hooked .Thanks for the links .

sweet , I got a rad bike that is EMP resistant . Let us know how your project comes along . Fiber optics in classic car sounds awesome .

I intend to do something similar, however because the CAN bus is so hackable (maliciously), I will use some other protocol over POF (Plastic Fibre Optics). That way I can protect against EMP attacks as well.