The 1984 SVO system seems to respond best with about 14-16 degrees base timing and approximately 16-18 PSIG of boost maximum. This engine strategy has its worst pinging in the "above 4000 RPM" range and will require high-octane fuel to keep the power up.
Most likely, if you have an 1984 engine, it will have many miles on it and probably have a considerable amount of hard carbon build-up on the port side of the intake valves. Adding more boost and octane may not increase performance results because the airflow characteristics are not very good.
If you replace the valves when doing a valve job, get the latest valves available. The 1985.5 and newer intake valves have a small dish in the combustion chamber side and a 20-degree undercut on the port side by the valve seat contact area which improves airflow through the whole range. The dish in the combustion chamber side also reduces the compression ratio which I maintain is a benefit for increasing on-boost power, with a slight loss of off-boost power.
The best power comes from retarding the factory camshaft by 4 degrees (which moves the torque peak higher in the RPM range), setting the boost pressure to 18-19 PSIG, advancing base ignition timing to 14-15 degrees and running a super-octane fuel blend. This combination of settings of the factory components will produce approximately 240 ft-lbs and 210 HP on a dyno!
I like to retard the factory cam by 6-8 degrees to bring the torque peak higher, and for street use, recommend limiting the boost pressure to 16-17 PSIG as there is not much pump fuel that can handle the detonation.
The 1984 strategy shuts off fuel at 6250 RPM as an RPM limiter so there is not much of a benefit to bringing the torque peak much higher than about 4000 RPM.
Reducing the exhaust system back pressure will improve throttle response and increase power through the whole RPM range. I recommend the Borla system which is available in either the single muffler design for the 1984-85 SVOs and in a dual muffler system for the 1985.5-86 SVO. The dual muffler will not fit the single muffler vehicle without extensive modifications, so I don't recommend doing that.
Exhaust system, higher boost, cam timing changes, port matching, the later exhaust manifold, porting the exhaust manifold, head porting, larger valves, ... are the order to improve performance on the engine assembly.
When getting the power up there with the REP-AF gearbox (4.0x first gear), there can be problems with its serviceable lifetime. I have been able to wear out the countershaft thrust washers in a relatively short time (approximately 15,000 miles). Switching to the REP-AG (3.50 first gear ratio) will help as it is a stronger gearbox and will handle more torque.
The original REP-AF gearbox (4.0x first gear) was rated to 210 ft-lbs of torque--which is what the stock 1984 SVO produced! The REP-AG has stronger bearings on the countershaft mounted in a reinforced gearcase and is rated to 250 ft-lbs.
The 1985.5 engine produces about 240 ft-lbs, so there is a little more margin with the later gearbox, especially if it is used in an 1984 SVO.
Now the bad news: the REP-AG box only came on the 1985 and later SVOs. No other car lines from any manufacturer! New boxes are not available from Ford and haven't been available since around 1987 in the SVO Motorsports catalog. The salvage yards may have some available and some gearbox rebuilding companies can build a box with that gearset which is still available from Borg Warner. Incidentally, the whole gearbox is available from B-W last time I checked, but they wanted to sell them in a pallet only--I think it was 25 pieces!
The REP-AG has the paper, three-piece synchronizer rings and shifts better than the brass pieces. Use Mobil 1 5w/30 engine oil in either gearbox.