Looking to make 300whp or more .
From experience with several SN95 Mustangs & with building a wide variety of other vehicles the most effective approach is
to address the specific area of deficiency rather than try to achieve some particular number or metric.
What if you get 300whp but you didn't actually make the car drive better in the process? It's impossible to compare horsepower in a modern car that isolates you from the road, governs itself down to ensure maximum smoothness and extended transmission clutch life with "lifetime fluid", etc. vs a 30 year old car that weighs hundreds of pounds less and doesn't blunt any of the edges.
The huge bottlenecks on these stock GT's are the intake manifold, the midpipe and the heads pretty much in that order... once those are addressed then there are other bottlenecks but you can't go wrong starting with those. 94/95 Cobra intake manifolds are abundant on ebay, in fact I'm about to put mine up for sale in a minute. Those are pretty much an on/off switch for your 4000-6000rpm range relative to a stock GT manifold. Aluminum heads save you more than 50 pounds of weight over the front wheels and the increased air flow over E7's even with the stock cam is substantial, you might discover you don't even need to spend the money on a cam (and timing assembly, and removing the radiator, etc...) .
My recommendation is start with a Cobra manifold, high perf midpipe if you don't have one already & replace your ECU with something modern that runs speed density (holley, megasquirt, aces, pimpx, whatever.. just
don't bother messing with your stock ECU in 2026 it's ridiculous) . That alone will make your current performance threshold unrecognizable and it's stuff you would need anyway if you wind up going farther. You might find out the car's a lot of fun to drive just with that, or you can put some heads on it and either a cam or a set of high ratio rockers (much less work, most of the same benefit). You'll end up spending half or less of your budget so you can spend more money on gas making memories.
In my opinion a large part of the charm these older pony cars offer is in their simplicity and comparatively light weight. You'd have to spend Dark Horse money to show horizontal SN95 taillights to a Dark Horse at which point just buy that car and save yourself all the busted knuckles or all the phone calls to the shop if you pay someone. If you start throwing weight and complexity at the car to hit some particular dyno number I think it makes the car worse and you won't enjoy driving it as much.
