Clutch fork

I believe the 390 and small blocks all used the "small" input, which is 1-1/16" diameter. Therefore the small block clutch fork will work, and be more likely to work properly with the small block bellhousing since that's what it was designed for.

Only the 427, 428, 429 and possibly later Rancheros used the "big" input from what I found with some quick research.