Don't know if it's interchangeable but I doubt you'll get 1800rpm with a 350. You'll probably get more like 2500-2600. I'm thinking that's not a big enough difference to justify the trouble. If you want 1800 rpm you might have to go with a taller gear set yet, which means you might need to have one custom made.
Not much help, I know, but you had me thinking for quite a while.
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