To know crank diameter, check the bearing markings. StD, +0.010, etc. But I would go with a new complete rotating assembly from a US supplier. Cheap insurance, and the opportunity to select stroke. Many options there. Hard to beat ported X heads if this is what it has, but I do like the weight redeuction of Eddy or TF heads now that they are available. Many advantages to Aluminum heads and weight is the enemy (quoting Mopar Action's Ehrenberger). Even though t 360 is overall a better starting point, I am a 340 person for 54 years. Got my first 340 (and still hae it) in 1969. Raced the snot out of it in SoCal for years and never broke a thing. Ran 13.40's @ 105.38 all the time in stock form. Out pulled a brand new 440+6 Cuda at top end at Irwindale in 1970. That surprised him. He thought I had a Hemi! Jaw dropping moment when he saw the 340.