To meet the demands of sixth-generation (6G) mobile networks, distributed multiple-input multiple-output (D-MIMO) systems employing geographically separated antenna units offer enhanced coverage, capacity, and efficiency. We present a practical and scalable four-transmitter D-MIMO proof-of-concept using coherent joint transmission (CJT) and analog radio-over-fiber (ARoF) fronthaul, achieving sub-nanosecond synchronization. Experiments with 50 MHz New Radio signals at 3.2 GHz validate CJT performance under line-of-sight (LOS) and non-line-of-sight (NLOS) conditions. Results show up to 10.42 dB EVM-derived gain in the near-balanced LOS case and up to 6.22 dB relative improvement over the best contributing single-Tx baseline in the investigated NLOS cases.