v-6 in early A-body

Dion, technically it would be the cam that gets the sloppy reading since the crank sensor reads off the crank mounted flex or fly and the cam sensor reads off the distributor via cam via timing set. If you use a scanner to set cam sync, you can read the cam position and watch it while engine is running and I have never seen more that 1-2 degree fluctuation and that was on a 150K with really bad timing set. When you set sync, you do it at 1500 RPM to remove the slack since a bit of fluctuation at idle wont affect anything.

I do agree that in your case, a front crank sensor would be very handy but probably more $$$ than the flywheel. MSD wont work(made in china) unless you run aftermarket pcm, which in over 500 HP is probably a better idea anyway. MS Pro would be my choice but its not plug n play or user friendly. In the end its just building cars and what works for each individual application. :D