There will be a few problems.
The #1's lever latch for the closed position is the triggerguard hole; a #3's is an internal receiver detent that the #1 lacks to hold a #3 lever closed.
The #3 lever was designed to fit with finger clearance for a straight grip, and not a pistol grip as on the #1, so most folks will find it difficult to insert even bare fingers between a #3 lever and a PG - exascerbating your problem is several ways.
I would suggest a refitting of the hook angle of the tip of the pivoting latch on your #1's issue lever, to gain a more positive engagement, as a first step.
Also - ensure that the engagement edge of the latching hole in the #1 TG is not worn, needing squaring or replacement.
FWIW, the experiences I am speaking from include owning several #1 & #3 rifles over the years, including a #3 that someone had installed a custom/aftermarket PG buttstock onto.
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