The Lucas starter on Woodstock, a 72 4/4 with a crossflow was a feeble device and not really capable of starting a high compression tuned engine at all.
A geared starter (mine came from Cambridge Motorsport) was a complete solution with less battery drain and a much higher cranking speed; expensive though. Good chance the pre-crossflow starter is the same fitting, and if you can get one at a sensible price, could transform the car. Mine turned the tuned engine faster than a Lucas one would turn a standard engine even with a battery so flat the ignition didn't work. I don't mind admitting that flummoxed me for a few minutes.
PS The starter 'jamming' with a low charged battery is more symptomatic of a lack of battery power - not a jam at all. The battery cradle in a 72 4/4 will take a high capacity version of the 038. Check but it may be an 018 or 016 - can't remember the number.
