I'd go with a hi-Flow Borla Exhaust and a set of Richmond Gear 3.73 gears. This will give you excellent performance on the street.

 

Personally, I don't think a 91 L98 is a good platform for a "once in a lifetime" dream hobby....if you have a small budget, live where they are more rare, and may not have local mechanics/facilities to "bail you out". Not trying to be negative so much as cautious/realistic. From what I know, a MAF car (which isn't in your 91) is easier for the DIYer to learn AND the L98's have a limiting intake/exhaust manifold setup. There's nothing wrong with modifying one if you're willing to bust it open and do some real changes but it's gonna be costly even if you DO learn how to DIY.

Really, for both LT1s and L98's, I think the best modification is a stroker. IOW, adding more cubic inches is the best modification unless/until you are looking at high-speed performance (which you ruled out with your comment about Dubai highways).

I would encourage another forum member with SD tuning knowledge to comment on the iterations/cost necessary to retune a 91 even when milder changes (like tubes/cam/headers) are installed....let alone anything more serious? IDK...which is why I put this out there. Even with my MAF setup, I learned it myself...but still can't resist trying something new to make it "more perfect". Point being, tuning can represent a decent portion of the cost. Since the OP is in Dubai, what additional obstacle(s) does that represent?

I think we should convey everything before leading a "newbie" from another country down the yellow-brick road. For example, a 3" exhaust for an L98? Really?

 

this is just me, but I'd start with a cam compatible with my goals, an upgraded timing chain set, an upgraded water pump and work out from there.

 

Because of your location I wouldn't go too crazy. Unless you have a good (L98/LT1) mechanic, once you do your DIY and screw something up that car will sit (months/years).
I would not open up the motor (ie: cam, 1.6 RR, etc). Either get cat back for sound or get long tube header and stay stock the rest of the way(I'm doing that with my LT1). I would check with another L98 owner, because I'm not sure how a '91 exhaust flows....LT1s are known to be free flowing(therefore cat back system won't add much HP).
Maybe do the gears...you can find a used D36 with stock 3.07 or go higher(3.55). Also consider a torque converter....

As someone mentioned, once the ball is rolling it WILL get bigger ($$)...ask me I know. Had the budget set and wham....$1800 to rebuild transmission.....when all is said and done I'm in C5 territory money-wise