Spin polarized transport over 5 mum long carbon nanotubes (CNTs) is observed in magnetically assembled spin valves with electrochemically deposited ferromagnetic (FM) electrodes. An annealing procedure is developed to produce stable devices with highly transmissive FM/CNT contacts. The devices exhibit magnetoresistance (MR) with magnitudes up to 4%, and the sign of MR is consistently negative. The temperature dependence is investigated and MR is observed up to 14 K. Bias dependence is also investigated, with MR persisting up to ~300 mV.