318 to 340, 904 trans.

Richie said
And the 904 should be able to handle a 420 hp 340?

Is it

Option 1: the original 904 that's 40 yrs. old and never been touched or is it

Option 2: rebuilt with quality parts and a good shift improver kit?

If it's option 1, no, it won't last long

If it's option 2, yes it should if it was done right