'67-72 A-Body 273/318 to 340/360 Swaps.

In 90% of all cases, when you swap up to a 340 or 360 from a 273 or 318 in the '67-72 A-Body, you need only change the driver's side bracket. Both right and left insulators remain the same. And, in most cases, the passenger-side bracket will also remain the same — as long as your 273/318 passenger-side bracket has four mounting holes. You need the fourth mounting hole because the lug pattern on the 340/360 is a mirror image of the lug pattern on the 273/318 (one in the front, two in the back on the 273/318, two in the front, one in the back on the 340/360). In a few cases, you will find that your passenger side bracket only has three mounting holes. You will either need to get another bracket with the additional hole, or, if there is enough material to do so, drill the fourth hole.

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