If I remember correctly the Monte was available with both the big and the small box. A '78 should have the SAE box, but later years had the Metric box.

I don't remember how I think I know those details, but I did once own a '78 Monte Carlo.

1955 1st GMC Suburban | 1954 GMC 250 trailer puller project | 1954 GMC 250 Hydra-Matic | 1954 Chevy 3100 . 1947 Chevy COE | and more...
It's true. I really don't do anything but browse the Internet looking for trouble...