If you use an ITR water pump you can use either the ITR or the GSR timing belt. All the bearings are the same. But you might as well buy new ones. But if your only using ITR pistons then you dont need to change the rod bearings at all, cause your not changing your rods. But if you get new rods you should get new rod bearings. You dont necessarily need to do a head job either, but it definately wont hurt it if you do! You'll want to get a new head gasket, and if you want to be king get some ARP head studs & bolts. If you get ITR cams then you should definately do a head job. I hope I covered all your questions.