Are these Pinus roxburghii ?
If they are, Wikipedia says needles in bundles of 3 and are 8 to 14 inches long. That is an awful long needle to try and create bonsai with. Yes you will get some reduction, but this tree will have the similar problems as Ponderosa pine in terms of excessively long needles.
If it is not Pinus roxburghii, what species is it?