All bobtachs on 3XX and 4XX machines, up to and including the 453, have horizontal (side) pins. The 463, S70, and the walk-behind mini track loaders (MT5X) use the vertical (bottom) pin setup. The two are not interchangable, as a new boom design was introduced on the 463.
I have seen two different Bobtach pin mechanisms used on the 440B: an early one that has a bar that comes out of the centre bobtach, and a later one (like mine) that has a bar that is offset to left side. This is the bar that attached to the locking lever.
If yours has the later style, I am hazarding a guess that your lever is froze due to the bell crank inside the bobtach being siezed on it's pivot bolt. There is an access cover on the back of the bobtach that allows you to access the bellcrank. Possibly some penetrating oil and a little heat will free it up. You may also want to try pressure washing or vacuuming out this cavity, as crap tends to collect in it.
HTH