[84LX89GT]

Getting the 1.7rr's over the stock 1.6 non rollers would probably give you approxamately 10 horsepower....that's what i've "heard" but i've never seen a dyno test or seen results. With your combo, those roller rockers would act like a slightly larger camshaft which in my OPINION would be a good match to your current combination.
Also, if you don't want to run emissions on your car, step up and buy a non-emissoins 600 cfm holley. The stock Holley-Motorcraft carburetor is jetted fairly lean (and you'll probably get pinging if you disable the EGR) and is tamper proof and is actually officially rated at 580cfm. I took all the emissions off of my '84 and put on a 600cfm non-emissions holley and it worked well without any jetting changes, although it probably would have bennefitted heavily from a dyno tuning session.
If you do decide to go with the 1.7 roller rockers, it's a GOOD idea to change out the valve springs and get hardened pushrods since you're in there anyways (i think you can use the stock length pushrods, but you should contact the manufacturer of the RR's) so that way you don't take any chances.
My '89 has 1.7:1 roller rockers and i'm pretty sure the previous owner didn't change valve springs or pushrods and i know he didn't baby the car and i've had NO problems with it so far (about 5,000, he drove about 30,000 with mods). So i would recommend it on my limited experience and from word of mouth it would probably be a worthwhile investment, since it broadens the power band to optimize your current combination and also reduces friction.
Good luck,