Are these interchangeable?

Use the second one pictured, the one w/o that hangy-down thingy, which I have long ago forgoten what it does.
Only one of those forks will fit on the 1-2 slider, and the other one fits the 3-4 front slider;any way up.
The 1-2 internal lever has to be matched to the reverse internal lever.
If that cover did not come on that box,then occasionally it will be difficult to engage reverse, on account of the clearance between those two in not sufficient. If you have no problems with shifting with the cover properly located by the one long-shank shoulder bolt and at least one other shoulderbolt snugged down, then this is a non issue.If you have troubles I can walk you through it.

As to the first cover pictured, I have seen a few of those, but it's function escapes me.Or rather the execution of it's function. Perhaps a picture of the box without the cover showing the internal reverse idler-gear, and it's associated shift mech. It's starting to come back to me...............