so is any cam gear or oil pump - ready to file up a new one of these are you?
Buying them gives you (generally) a better product, designed to do the job, and with the correct attachment parts. Modification of the locating holes/pins is quite common as there are so many different types out there that they only make a small number and leave it to the shop or buyer to modify to fit.
Try pricing up new diff U-bolts and you'll soon see that most of these kits are pretty cost effective.