Can you define "weak"? Weak as in squats under accelerator, or weak as in bounces/doesn't control body motion well?
The stock springs do allow squat under acceleration, so that's normal. Can be addressed through uprated springs at the price of a bouncier ride (in my experience).
Might just need the stocks topped off, or replaced. I'd highly recommend Peter and team at NOS Import in WI, replacing the shocks with a good pair of his might just work wonders.
I'll let others weigh in on tube shocks, but you need to consider the way the load on the car will be changed and how you'll reinforce that area.