If your suspension is already lowered, the thing to check for is the rear anti-sway bar. A rear bar makes the car steer neutrally.
The pre-88 suspension with an added sway bar actually performs pretty well. I wouldn't spring for an 88 suspension unless it really needed it.
I would try the current suspension first
If you are planning on competing with the car, be prepared for increased costs due to the inevitable breakage of 30 year old parts.
Also, each governing body has its own rules so adding a non-stock brake system could impact qualification.
Sounds like you have a goody there so congrats to you.