The problem with existing systems is often the poor state of the rack and wheel boxes as well as a tired motor. Modern wiper systems for kit cars are readily available and transform the original system on the 2-litre cars. Stick with the existing wipers or, if you are serious, fit a modern system.
Such a system comes from Stafford Vehicle Components. It can be adapted to use modified original wheel boxes so no changes to the holes in the scuttle. A fair amount of fettling required. It’s not a direct swap. Once set up it is superb.
Holden’s and J&L Spares who recondition wiper motors may offer alternative approaches.
On the other hand, just disassembling, degreasing and re-greasing the various parts of the Lucas system will often speed things up and make the mechanism more vigorous. Motors also often need their commutators polished and the grooves between commutator segments deepened so the brushes make good contact with the brass segments. Relubrication of the motor bearings almost always helps speed them up.
Useful information on the Lucas DR1 and DR3 wiper motors as installed on the 2-litre and Jaguar XK 140 cars is contained here.
Steve Hunt often has reconditioned motors and parts for sale. He has a shop on ebay and his contact details are