crank sensors

[James W. Swonger]

 What about the other end? Every engine has a nice, big flywheel or flex
plate (which all have a multitude of teeth you could even pick a pulse
train off of). The indexing of TDC might be trickier. On the flex plates 
there are usually some uniquely-positioned holes which would serve.

 If you want something to bolt onto the front, though, I guess a
chopper wheel is the way to go. A thin steel plate between the crank
pulley and the balancer could be added without disturbing the balance.
Holes to interrupt an optical or magnetic path. 

 Is the intent to produce something universal? That might be a lot 
tougher. Most of the aftermarket crank trigger kits are universal -
will fit any small block Chevy.