OP: You did not mention what size grab hooks you installed. 5/16" grab hooks are the most useful size. 5/16" hooks will grab 3/8", 5/16" and 1/4" chain securely, from my experience.
If you have
3/8" grab hooks they will grab
5/16" chain too.
Home Depot in Florida has a best package price on chain: Grade 70 / 4,700 lbs working load limit,
5/16" X 20', with two Grade 70 grab hooks for $37.98. Chain and hooks are made in China, which is a quality control / safety concern for some. Likely similar price in other states. My receipt is dated 8/07/2012.
Chain unit packaged in a tough plastic bag labelled "TOW CHAIN WITH GRAB HOOKS" in the chain sub-section within hardware.
I have a Kubota B3300SU / 33-hp / 1,800 pounds; one Kubota increment smaller compared to your tractor. I would not buy heavier [literally] chain than 5/16" / Grade 70. Your
tires will
loose traction before you approach 4,700 pounds pulling force.
Have Home Depot cut the 20' length so you have one 8' length and one 12' length, add two Grade 70, 5/16" SLIP hooks from Tractor Supply and you will be ready to work. ( My Gainesville Home Depot inventories only Grade 43 slip hooks.)
If you are going to drag many logs get a Hanging Tree setup so you do not hurt yourself. Northern Tools sells the 3-point ready Norwood Log Hog, Part #41255 @ $300. Mine comes from OMNI Manufacturing which sells direct and via eBay. See following link including safety information:
OMNI Manufacturing / OMNI Grabhook Hanging Tree