Basically 4 different SB rods used through the entire production run includeing the poly 318.

1. The 273 and 318 through 71 used the lightest version with bushed small ends.

2. The 340 came out with a slightly beefier rod (all other rods were variations of this one)with a bushing and floating pins.

3. Some time in 71 they came out with an unbushed 340 rod for use in the 360 and 318 until 92 for the 318 and 93 for the 360.

4. When they went to magnum engine desighn in 92 and 93 they used the same basic rod still but they narroed the top end.

All rods are the same length and journal diameters. You can use the magnum style rod in ANY older SB (balance should be checked). The pressed fit 318 360 LA rod can be used in any other SB (they need narrowed small end to fit in a magnum). The early bushed rods can be used in any engine with floating style pistons, some 340 guys will run the lighter 273 318 floating rod to lighen it up, I have seen some of the heavier 273 318 rods that weighed as much as the lighter of the 340 rods, the weights are all over teh place.