First I've heard of it.
Ideally (in my opinion), you would want to have an alignment done at a shop that frequently does 993s. They need a special tool to set the kinematic toe. If it persists, then consider changing the suspension (the shocks may also be shot. This way, if the alignment fixes the issue, it's the cheapest solution. My car handled just fine at speeds up to 120 at the track with stock US suspension - until I upgraded to PSS-9s
The problem with this scenario is that if you decide to change the suspension, you need another alignment and at $300-$500 for an alignment it's a waste of money.
If it was my car, I think I would opt to switch to the Euro M030 suspension (new shocks and springs and a lower ride height and not too expensive) and then have it aligned to RS spec. The shop may ask if you want the caster set to account for the crown in the road (they don't set the caster equal on both sides). I'd decline and have equal caster to each front wheel.