I don't know if I'd even mess with the shifter interlock given the way we use these cars. Unless you just like a challenge and have plenty of hair to pull out.
I'm certainly given to taking challenges, and I've a full head of hair with which to work. The biggest issue seems to be finding the right column, since it's a one-year-only piece. Thing is, I'm working on buying
yet another car. It's a 1970 model, and its rarity somewhat demands an accurate restoration. It's one of less than 20 of its kind.
Part of me wonders about the cross shaft too. Just because the factory made them different doesn't mean you can't get lucky and be close enough to work. Especially given the way the bushings that it rides in are made. If the 904 has enough width to ride on both sides it doesn't necessarily have to be *right*. It just has to not bind up, and not fall out.
From what I've gathered in my research, it seems that guys have used the Slant Six and LA lockout countershafts on larger engines with pretty decent success. It goes something like this: The shifter, regardless of its fore/aft location, is consistent in its transverse position, i.e. regardless of which transmission/shifter you have, it's the same distance from the frame rail on your given model. As such, the A-body Slant Six countershaft is longer beyond the arm that connects to the shifter, but the distance betwixt the two arms on the countershaft itself is the same. The link between the countershaft and shifter is also the same, assuming the same transmission (the 3-speed link doesn't fit the 4-speed, etc.). So, you lop off the end of the countershaft somewhere beyond the bellhousing-side support/bushing bracket, assemble, and smile.
That being (supposedly) true, it would stand to reason that since both the A904 and the A727 use a virtually identical valve body, also at a consistent distance from the frame rail (roughly centered in the transmission), that the difference between any of the three possible transmissions for a given body style (Slant, A, or B/RB) would also be on the far side of the arm that operates the transmission via the lower link. Shortenening it beyond the bell-side bracket
should work. The lower link from the countershaft to the transmission may be shorter; I haven't dug into the automatic stuff.
Fun Fact: In 1970, the console
automatic cars had the ignition interlock as well. The interlock linkage for floor-shift cars is simply the column-automatic shift linkage. It's connected for the same reason: You can't remove the key unless the transmission is in Park (rather than reverse on a manual).