the stock turbo, full exhaust and injectors/pump have to be replaced to get to even 300 crank hp.
For 300 awhp on the RG Mustang all wheel drive dyno, you will need a GOOD Evo 16g, cams, full exhaust, good intake, injectors, pump and front mount intercooler with some sort of means of tuning. Probably methano/water injection as well. It would be easier with a slighlty larger turbo as there are only a couple of actual 16g cars making over that and they are tuned very well, and have lots of time on them making them that way.
220-250 awhp on that dyno is a pretty damn fast car. My car was making a "mere" 291hp when I went 11.92. Just for reference. Also for referece, Subaru STis routinely make between 205 and 210 on that dyno, so again, no need to go that far for a real, tame street car.
your car will feel very fast with a full exhaust, a ported 14b(stock turbo from a 1st gen car), some 1st gen turbo cams and a good intake system. If you add a fuel pump and some mid sized injectors with a chip tune or an eprom tune or something conservative in the engine management dept, your car will feel pretty damn good and in fact it will be.
This I think, with a few minor changes/additions would make for a perfect daily driver, quiet adult ride.