I found my issue and its a Goodie !! Its Almost a Lonnie one.....

The ignition box I was testing with has an issue with the tach lead - it produced an odd low voltage noisy signal. - I changed ignition boxes and all of a sudden the RPM readout worked. It does need a small cap to filter some of the noise (power supply?) out to prevent a bouncing reading but on the scope it has a very normal looking pulse - Will look into it further but its an old ignition and i'm not sure if it might have been previously mistreated..

Anyways - A successful trip down the OpenX Rabbit hole and we will have telemetry from the boxer when it runs..

EDIT: sorry - testing was early this morning and I forgot that it was connecting the ground that solved the issue not a cap ... I am assuming if you use a Cutoff switch the ground gets through to the radio (and OpenX) via the cutoff when its set to run. I had to connect the ground to get a normal reading.