318 crank into 340? pitfalls

Just some notes on your costs.... what does 'true up the rods' mean? And the 340 uses pistons with floating pin & retainers, not pressed-in pins, so no need for the press cost, if you assemble them yourself.

With your build date, it is hard say if it is an early or late 340. Does you damper have an obvious imbalance on the front surface, and have the words 'for 340 only' cast into it? That would be the later 340, with the cast crank.

From the factory, the early 340 will be close to 9.75 static CR. For the 89 octane, you probably want to drop the CR to 9.0 or so, IMHO. There are H405CP pistons made for lower compression. RockAuto shows a set for $150-160. And Silvolite has their 1267 cast pistons for lower compression; Northern Auto lists sets in .020", .030" and .040" oversize for $184. Both of these pistons will drop the CR to between 8.7 to 9.0, assuming your block has been decked around .005"

I seriously doubt you will get as good an engine built for the same $$, with the parts right and the machining done reasonably well. I don't see where building a 360 will be any different in price; it is just if you can realize a profit on the 340 parts vs a decent 360 core. And the value of your parts depends a bit on if it is an early or late 340. A 340 in an A body does have a certain added value for the non-engine knowledgeable types who buy these cars so I agree on that point.... you ought to see the slobbering and hear the 'oooohs' when my son mentions a 340 in his '65 'cuda LOL.... even though the 340 did not exist in '65 and the only 340 part left is the block, there is just a mystique around this engine.

Did you ever look up the 7 digit casting number on the sides of the rods? Just curious to see if they are the heavy or light rods.

Sent you a PM.