The late 316 tractors with the P218 Onan engines are very nice, but the 318 with the dual spools of hydraulics, power steering and the turning brakes are enough of an advantage that migrating your 316 parts over to a 318 makes a lot of sense. Too bad you missed out on the steering valve with the parts tractor you just scored...
Adding the H2, power steering and turning brakes to your existing 316 frame can be done, but is a lot of work that would not be needed if you get enough of a 318 together to go back onto that frame you just got.
Let us know what you decide, and pictures are always fun to share...
Chuck