What size engine would have a block # of SR82018

SR is a service replacement block. The number after it should be the original block number. Dealers were supposed to stamp the block when it was installed, with the car's original block number. (In theory, anyhow). So what you have is NOT the original engine. Distributor casting numbers: one is the date code, and it translates to August (H) 29, 1966. So the engine may predate the car. That's not unusual as the 1967 service replacement blocks were cast during the production run, and stored until needed. In other words, it's a true 1967 block, just cast in 1966. Moving on: The other number is the casting code. In general, if you see a "pyramid" casting near the distributor, it's a 326-421-428-455 family. If no casting, it's either a 389 or 400. For 67, it could only be a 400 since the 389 was retired in '66. So....I could not find "36339" either... but check that area carefully. The casting may be worn or badly stamped. I have a feeling it's really "9786339" which would be a 326 with a single 2 barrel. It was a popular engine and came with either a 3 speed manual, 2 speed powerglide or Turbo400 trans. Good luck!

If it's a pontiac engine the engine size should be raised numbers on the side of the block .

Pontiac only cast the displacement on the blocks starting in 1968. Prior to that, you have to work with the distributor pad stampings. I have the shop listing for every engine, I'm willing to bet its casting #9786339 which is a 326 2 bbl.