Just put the cover in any gear, then try the OTHER lever and see if you can get a second gear.... Which you should not be able to.
In the late style cover with the scissor interlocks, you have to install the forks and then it is impossible to get two gears simultaneously.
But the early covers will get two gears if the interlock lock-out pin goes missing.
With either cover, after it is on, and with at least two of the big-shoulder bolts installed, push the cover "up" as far as it will go, tighten them, then make sure that reverse can still be easily selected.
Make sure the oil baffle is installed in the tail under the vent .....
Did you replace the O-ring on the reverse shifter shaft? You have to remove the reverse idler gear to get that thing outta there. That can be a PITA, so that O-ring may get overlooked during several reconditions and eventually it leaks. Sorta like the back-up light switch which leaks right thru the bakelite seal on the contact spades.
Good on you for doing all the other tricks.
That is so cool