If the engine is stock do not install higher-flow injectors. In fact, in some cases, bigger injectors on stock engines decrease part throttle performance and degrade drivability. Also, on a stock engine, throttle body "flow boosters" (also known as "air foils") make no contribution to performance.
On a modified engine, larger injectors and TB "flow boosters" may or may not improve performance. It depends on the level of modifications.
As for a tune-up on an L98...
Change the spark plugs, the distributor cap, the rotor and the plug wires. Service the air filter. Check the base spark timing and adjust as necessary. Change the drive belt.
Clean the MAF Sensor (if equipped).
Run three bottles of Red Line Complete Fuel System Cleaner though the engine using one bottle per tankful of fuel.
Change the oil and filter.
Change the coolant.
Change the power steering fluid
