Yes, the crankshafts are all directly interchangeable from '60 through mid '76 (when forged cranks were introduced), with the caveat that an LG block (170) will only accept an LG crank (170), while an RG block (198/225) will accept an RG crank (198/225, keeping in mind the 198 and 225 use different-stroke cranks and different conrod lengths). Cast cranks cannot be installed in pre-mid-'76 engines, nor can forged cranks be installed in post-mid-'76 engines.

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一期一会
Too many people who were born on third base actually believe they've hit a triple.

I have seen several people post, about machining the early crank to the late model hole size. I have to question if this can be done. There is a pilot to locate the flexplate. I don't know it this will be a problem or not. I will measure this tomorrow, and see what I think. Has anyone actually machined the hole in the early crank, and verify, that it works?[/quote]

OK, I went out to the shop, and looked at the early crank, and it does look like opening up the hole in the end of the early crank, to the late crank size, is a viable option.
It will make the flexplate locating pilot thinner, but I don't think it would be an issue.

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Charrlie_S
65 Valiant 100 2dr post 170 turbo
66 Valiant Signet 170 nitrous
64 Valiant Signet
64 Valiant 4dr 170
64 Valiant 4dr 225

So engines built post mid-76 had cast cranks and earlier engines were all forged, correct?

Too bad I can't just pull the crank from my current engine and work it, but I'd like to be able to drive the Duster while I'm prepping the new engine and tranny for installation.

So okay, I'll obtain a forged 225 crank from a early/mid 70's engine, have it dynamically balanced along with the pistons and rods, get 'er installed and I'll be set to go for tranny installation once the new one is rebuilt and ready to go.

While the engine's on a stand I oughta install a Dutra oil pump as well...

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'74 Duster w/ HEI ignition, beat to snot suspension, A904, 8.25" 3.55 SG rear, still being tuned up and gets 17 MPG

Know how they always build a better idiot? That's me

Yes.
'68 through mid '76.

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一期一会
Too many people who were born on third base actually believe they've hit a triple.