Delica Canada | Mitsubishi Van Club

I had the alignment done on my '91 L300 to these specs:
1987-1996 models
FRONT WHEELS:
toe in 0 degrees 12 mins +/- 12mins
camber 0 degrees 30 mins +/- 45 mins
caster 3 degrees +/- 1 degree

I can't find the report, but I recall the results were close and tire wear seems to be very good and even. However, the van does not want to hold a straight line when there is any crosswind. It can get quite jumpy and I find it concerning/stressful at times.

I'm thinking of just adjusting the toe-in angle by maybe 1/4 turn each side (1.5mm, .06") myself... that should improve straight line tracking, but what are the chances it will significantly increase tire wear? Or am I off track completely?
I suppose I could take it back and have it adjusted, but it's such a hassle and it seems like such a simple thing to do.

12mins is about 3mm total toe in. If you add 1.5mm of extra toe you'll still be within the +/- 12min, so I wouldn't expect tyre wear to be out of the ordinary. Assuming the alignment shop adjusted it to exactly 12 min then you could get away with half a turn before you're out of spec.

(And yes, I checked your math. A quarter turn on each side does add 1.5mm of total toe.)