That's not good, shut down when knocking becomes apparent & a fix can be cheap.
Had to have it done years ago on an engine I'd had rebuilt. 1,100 mi. round trip, and it started knocking about 250 from home. New rod bearings right there (in frame job) and it lasted 'till long after I sold it. Shop that had done it gave me a replacement crank & bearings set I gave to the next owner. (No time to do it or $ to have it done at the time)
Zetec or SVT bottom end could be the basis for a rebuild, SVT heads take more of a beating from timing belt problems so they're harder to find good. Once you hole a block, the bottom is pretty much trash.
I had proof of a goof when my old Jeep went in similar circumstances, shop installed & tested it & the Dealer who repaired noted rod caps on the wrong rods (numbered).
This one - sounds like you did the install, IDK whether it was spun to get oil pressure before putting in the plugs & firing it up. Some help towards getting the bearings checked/done when it was knocking would have been good, split responsibility without proof either way for goodwill.
Can't really expect any more than the equivalent of that at the best IMHO at this point, bleeps that it's broken but I don't want to raise hopes that are unrealistic.
Depends on the Seller's good graces & what your deal with the Seller was to begin with as to any possible help. Again, I don't know the deal made or the price paid to even guess at that.