Ok I have the correct converter for the small 273 registry , so I guess I need a small registry flexplate also to fit the 273 crankshaft , correct , does anyone have the correct hole size for the flexplate .

Let's try this , I have a1966 273 engine with a 904 transmission . The crankshaft has the small registry hole for the converter. I have the correct converter and need a flex plate . My question is will a 1968 and up flexplate work or is the the registry hole in the flexplate a different size for the 1966 .

Crankshaft is in machine shop was trying to get the correct register size before it came back while I had the extra time , will have to wait for it to come back and try the 68 flexplate.

Ok , took the 1968 flex plate to machine shop and it fit the 1966 crankshaft perfectly , thanks

For what its worth, as long as the flex plate fits over the crank flange, the larger diameter register flexplate still works on the small register flange. The 6 bolts will hold it fine. At least it did on the one I beat the crap out of for nearly 60,000 miles.

Sorry, late to the game.
I thought the change in the register diameter was done in 64/65. 66 should have been the later version.

For what its worth, as long as the flex plate fits over the crank flange, the larger diameter register flexplate still works on the small register flange. The 6 bolts will hold it fine. At least it did on the one I beat the crap out of for nearly 60,000 miles.

Sorry, late to the game.
I thought the change in the register diameter was done in 64/65. 66 should have been the later version.

For what its worth, as long as the flex plate fits over the crank flange, the larger diameter register flexplate still works on the small register flange. The 6 bolts will hold it fine. At least it did on the one I beat the crap out of for nearly 60,000 miles.