Glad to see the swap is underway kv1! The kits you posted look good, Fel-Pro is quality and the fuel line kit appears to be alright.
The best I can remember, the batteries are hooked up parallel. The other battery will have to go on the opposite side of the engine bay. I suggest using 1/0 pure copper battery cable, as it was suggested by my 6.2 K5 Eskimo buddy, Koots
mainly for better power transfer. In fact, I have our entire conversation over at ChevyK5Blazer.com still saved where he was giving advice on all I needed for the swap. You are more than welcome to it, just ask!
Fuel pump - Carter P4070
Starter - I have found them sub $100. Let me look around and I'll post my findings.
Radiator -
AC Delco 20958 GMC Chevrolet G Van Radiator 1985 1991 6 2L V8 Diesel | eBay
Buy this one if possible! It is a great deal! It list for a 3500 Van, but it gives dimensions. Measure and check it's fitment before scooping it up.