I don't understand how feed line length would result in high SWR using a dummy load at VHF or UHF, unless the load or coax are way out of spec.
It is true that loads are transformed by feed line length, but even a 75 -j50 dummy load (grossly out of spec!) would only result in 2.4:1 SWR at the radio using either a 0.25 or 0.5 WL feed line (and odd multiples of) at 146 and 432 MHz.
Steve, W3AHL
Steve W3AHL