Yep, the 3600 series (3/4 ton) came with the 216. The block casting number is on the passenger side of the block, down low (almost to the pan) just in front of the distributor. I don't know if inliners.org has head casting numbers, but you might check. I'm sure someone on the 'Bolt will be able to decipher those for you.
On the VIN,
J = 3600
53 = year
K = Kansas City, MO assembly plant
Your last six numbers are the Plant Production Number, with the first truck built at a given plant receiving the number 001001. So your truck was number 20,169 off of the line.
All of the VIN info comes from
Don Moen\'s 47-54 Serial Number page
