You would be very close with the estimate of the weight,I don't recall any other attachments for these apart from a blade,F W McConnel was the only one who made a dual purpose machine with a flail head for hedgetrimming being available.
As for the pto speed well they are " rated for" 540rpm but to be honest only run them at a speed that you are comfortable to operate it at,For their time they were better than a shovel and I would not recommend pricing a muck shift with it,if you have any reasonably hard digging then a 3ton mini will out dig that and may more of its relations,O! they are not recommended for tractors with cabs,more than one man lost his head to them .
the second hole was to allow drains to be cleaned ie allows a deeper depth but not a lot of height .