As part of the gearbox change I swapped the propshafts with known good ones to take away the chance that they were imbalanced, I have since removed the housing from the disc handbrake to ensure that wasn't causing it. The power steering box has been changed along with the coupling shaft (the old one had play in the UJs), with that the drag link was changed with different ball joints. These are all parts that were previously on Keely with no issues.
I've checked for bearing play on all four wheels and swivel play on the front two, I didn't find anything out of the ordinary. The wobble is intermittent over 40mph and varies in amplitude, if it isn't wobbling there is no effect under braking so no warped discs and braking doesn't stop the wobble so no loose bolts on the disc. All drive flanges are tight.