Measure the distance between the flange of the starter, where it meets the bell housing and the centre of the bendix drive gear, when fully actavated.
Now measure the distance between the bell housing starter mount face and the centre of the flywheel ring gear.
The second measurement tells you where the bendix gear needs to be on starter activation, the first tells you where it is.
I used a std escort starter and machined the flywheel ring gear mount stop back 13mm towards the crank.Or as Mickas says you can space the starter back, the down side is the starter has little clearence as it is, with out spacing it. This would also depend on your exhaust down pipe.