Are 340’s rare

Not all 72 340s had cast cranks. Some 72 cars had 71 blocks in them and if they did---they came with a forged steel crank,forged steel I-beam rods and light not HEAVY cast aluminum pistons---8 and a half of course on CP ratio and smaller 1.88 intake valves. The 71 blocks had more meat and could be bored more. I once had a thin casting 73 340 that I degutted and regutted with forged 1051 steel crank and I rods and 10 and half cast aluminum pistons with a pair of cast in 67 for 68 model year 64cc X Heads. That TX9 73 Duster ran like a Raped Ape out of HELL!!! The Coppers used to call my car the Black Hole because I would always disappear from sight.