85 5ktq in rally cross!

[Livolsi, Stephane]

Ooooh! This will be a blast.
 
Now that my daily driver is the 88 5ktqa, Tihol and I are going to enter
the 86 5ktq sedan in a rally cross in Ashcroft Feb 28th.  (it already
has a dented fender anyway)
This particular rally cross is an ice race on a frozen lake.
 
I need list help/knowledge on the diff locks
When I replaced the clutch about a year ago, I broke off 1 of the
nipples on the center diff lock actuator.  At the time I just plugged
the hole to keep the insides clean, and plugged the vac line - (never
used the diff lock anyway).  I think I'd like to have the diff lock
working for the rallycross.
 
So, can I just reach under there and manually pull the actuating arm to
engage the diff, then unengage it for the drive home? or does the vacuum
actually hold it in the locked position?
 
Any info would be greatly appreciated.  we'll be working on a fixing up
the car this weekend. 
 
Stephane