So... What did I buy?

[crackedback]

Might take some doing to get the crank balanced using the 340 stuff. Get some really light pistons if using those chunky rods. I bet an aftermarket set of rods and decent pistons would get the bob weight pretty close to the OEM 318 bobweight.

Stock 340 rods are about 760 grams IIRC. Don't recall what 318 rods weigh. Aftermarkets like Scat I beams are in the 600-620 area IIRC. Other may be even lighter.

 

[NC Engine Builder]

Here is a old school TRW forged piston, pin, and factory 340 rod compared to a icon forged piston, pin, and scat rod. This difference is staggering

 

[Oldmanmopar]

1967 - 1972 273 and 318 had a narrower connecting rod beam width and lighter then 340 , 360 rods. 1973 and later all had the same beam width rods.

But no forged cranks after 72. The forged crank you pictured is a pre 1972, 273. 318 That is why the journals are not drilled. Because it was from a narrow beam connecting rod engine.

 

[str12-340]

But they should have a round medallion (IIRC) glued / attached to one side of the block

Are you talking about a rebuilder's medallion? The only time I have seen something like that is a medallion that rebuilders use. Whatever they are stuck on with comes undone at a specific temperature so they know if you managed to overheat the block - no medallion, no warranty.

 

[Oldmanmopar]

Smaller rod's? I've always read that all the small blocks have the same length rod and take the same rod bearing. Please explain this

Narrower beams which made them lighter. All the rods were the same in length and the big and small ends were machined the same. So they would all fit. Just a weight and strength difference. Forged cranks without the journals drilled were for the narrow beam rods.