I've just finished upgrading the suspension on my 1990 Rev1 NA SW20, I've been reading the Toyota MR2 Performance book and it provides some wheel alignment specs.  It recommends front toe out of 0 to 1/8" (0 to 3.2mm) but it recommends rear toe in of 3/16" (4.8mm).  Here's the questions, is the rear toe in setting 4.8mm per side or 4.8mm total?

I don't know anything about the 'performance book' but 4.8 mm per side would give bad tyre scrub. 
 
 
 

IIRC, the BGB suggests 6mm total toe-IN at the rear. This seems excessive, but I think the early version of the SW20 tends to dynamically toe-out as the suspension shortens (ie weight on outside wheel in a turn). Later SW20 does this less so presumably doesn't need so much. The problem of the dynamic toe-out is it encourages the rear to let go. If you have other solutions to this (stronger springs, wide tyres, swaybar and other suspension geometry adjustment pieces) then you can reduce the toe-in to say 2 or 3 mm total and get more life out of your tyres.
 
 

The '91 service manual says 5 mm total toe in for the rear and 1 mm total toe in for the front. (see pic)
On my '90 NA these settings give good handling, as well as very even tyre wear right across the tread on both front and rear.