My two pennies worth. You need to cross the threshold at 50ft. Add that to the threshold elevation (54ft) gives a height at threshold of 104ft (round it 110ft for ease of calculation and safely). To achieve that requires a ROD of 325ft/min from 1900ft at 5.5d from the threshold. If you then project this profile back along the approach you would have to commence the descent from 3000ft just inside 9nm from the threshold or 3.5d from the beacon.