We have recently succeeded in measuring the excitation spectrum of charge doped cuprate chains with a 90 degree Cu-O-Cu bonding geometry. This study resolved a long standing controversy over the existance of strong ferromagnetism (~20meV) over such bonds and thereby supports multi-orbital quantum chemistry approaches which also succeed in describing the correct exchange parameters in the cuprate spin ladders and high Tc materials too. However the most interesting aspect of our study was the observation of charge induced discontinuities in the excitation spectrum. We aim to attain high quality data on a sample of 20% doped chain and 30% doped chain. A delicate balance between charge and spin hopping energies is anticipated making this an ideal model to test the importance of electrostatic screening on the hole doped Hamiltonian. This provides a route to a full cuprate Hamiltonian.