Lots of threads on here that discuss Cat's SystemOne undercarriage, I would say none of them are very positive. It all depends on how many hours you are planning on putting on the machine per month, year, etc that could be the main factor in your case. If the dozer doesn't have to earn a living you could possibly make SystemOne U/C work.
SystemOne can be converted to "conventional" Heavy Duty undercarriage but a) it's not a straight swap (some welding & fabbing involved), and b) it won't be cheap because everything in the U/C is different between the two systems.
On the plus side HD undercarriage opens up a world of aftermarket suppliers where Cat is the sole source for SystemOne parts.
You pays your money...……..