If you had a 1977 B-210 hatchback it probably had a 63a dogleg box, why dunno, that 1 year they decided to go way overkill on the transmission.

the differences are the shift pattern, the clutch slave is on the other side, the 63a is heavier and built a little stronger. It uses a different, larger output shaft, like the automatic tranny.

Other than that they're the same, basically. if you had a 1200 it would be annoying to fit, but since all 210's had an "automatic" transmission tunnel ( they were all big enough to fit an auto ) it's more or less a direct swap.

there was possibly a 63a with a 1:1 5th gear instead of the overdrive 5th that's common.

The wiki has a table of how much power the 56, 60 and 63 boxes can handle.