67' 318 crank in a 69' 340

I have not gone back through all posts but the KB243's were what I was using for bobweights in post #43 and beyond... DUH! I see I said KB167 from that post onward but meant KB243.....sorry for the confusion! You ARE paying attention; awesome!

So, recapping: if you used the KB243's and stock 340 rods, they will be a tad heavy for the 318 crank.....around 2160 grams bobweight (And, I forgot to add that the more oversized you go the more the pistons typically weigh, so that bobweight gets a bit further off.

I'll put this idea in front of you again to chew on: Buy KB43's and SCAT rods. Then your bobweight will be well under the 273/early318 target bobweight; it is around the 1893 grams I cited before. What I like about this is:
1) if you recondition the 340 rods, you will be spending about 1/2 to 2/3 of the price of the new SCAT rods
2) The SCAT rods come weight balanced end-to-end and for total weight. So no money is spent on balancing the rods (which gets done on a performance balance)
3) The balance work becomes 50% -70% cheaper because all the machinist needs to do is weigh one piston-pin-rod set (with rings and pin locks) and compute the bobweight and balance the crank to that. Done. Between this and the savings on reconditioned rod work, you have paid for the SCAT rods.
4) The lighter weights save on stress on the rotating components with all those benefits. And with a 4 speed, things will rev better, and shift better: when you shift, the lighter rotating mass will make the synchros work less... faster shifts.

That is the route my son and I went on his 340. The crankbalance was something like $95 total....CHEAP! I weighed the pistons/rods/etc. myself and gave him the bobweight to work to so that saved some cost. But him weighing the parts and computing the bobweight should not be much time or cost. He took off about 82 grams IIRC from each of the large end counterweights and that was that.

So we have been down this road before....