Here is the 1955 Illustration notice it also shows a difference in the lower sheet metal for the 223 Six this moves the support further forward,ask any one that has done a 302 swap in a car that had a Six vs one that had the y-block and you will find out it is a little over 3".
I have both a '55 with 272-V8 and a '55 with 223 I-block 6. The front wall halves on each side of the radiator support are identical and so is the radiator support itself. The factory stamped extra holes in the sheet metal pieces and mating holes in the radiator support for the horn mounting brackets on the 6-cyl which are mounted down lower.
The front splash pan painted argent silver IS DIFFERENT on the 6-cyl as it has a cut-out for the bottom of the radiator to slide down into. The splashpan on the V8 runs straight across.
Bottom line, you can use the exact same radiator support and front wall panels no matter which engine you have. If you have a 6-cyl, you MUST use the 6-cyl splashpan. If you have a V8 in a car that originally had a 6-cyl, you don't need to swap out the splashpan, but there will be a big void over the radiator support where water will run down and rot out the bottom of the radiator support. If you have a 6-cyl in a car that originally had a V8, you do need to swap out the splashpan or you will not be able to install the 6-cyl radiator. You can't use a V8 radiator with a 6-cyl, because the fan will hit the engine.
ALL the difference is in the side mounting brackets on the radiator.
There is a round rod with a hole on each end that bolts to the top of the radiator support. On the V8, that rod mounts in front of the radiator. On the 6-cyl, that rod mounts behind the radiator. Same rod, just mounts differently. Horn mounting brackets are also different because if you tried to keep V8 horn brackets with a 6-cyl, the radiator will hit the horns because it is pushed forward. Same horns, different brackets, and the mount lower on the 6-cyl. That is the reason for the extra holes in the front wall panels and the radiator support.
If you are converting from a V8 to a 6 or vice versa, you need to pop out one threaded insert from the square hole on each side of the radiator support and re-insert it in the blank hole a couple inches away.
You battery tray mount is also exact same part regardless of engine. It has extra holes mating those horn mounting holes. It is wonderful.
