Replacing ‘67 273 with a ‘78 318 questions

Bobacuda said

I’ll have to remove a couple of acres of New Mexico and oil from the trans to find out what year the 904 is. I suspect it came from the junkyard with the 318. How can I tell if it needs a annular ring? BTW, what does one look like - I’ve never heard of it.

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The snout on the TC is smaller diameter for '67 and earlier, than for thr '68 and later TC snout. So if that early TC was used, then a thin ring would be installed inside the larger, later registration hole in the back of the crank to fill in the gap in the diameters.