underdrive pullies

[Mr 5 0]

pxcr_600:

Underdrive pulleys are fairly cheap (as performance mods go) at $100. or less and are worth from a 5 to 10 HP increase.

Your '85 could really benefit from a true duel exhaust system, possibly from a later model. Losing the catalytic converters would help a lot, if emissions aren't a problem in your state. High-flow cats are another option when replacing the exhaust. Cost a lot more but are legal.

Of course a better intake and carb tweaking wouldn't hurt HP a bit.

Your stock engine was rated @ 210 HP in '85 so you need another 90 HP to get there. Not easy.
Subtracting 10 for the pulleys and maybe 15 for the exhaust you still need another 65 HP to reach your goal. Aftermarket heads and intake would get you close but thats fairly expensive, as you know.

I would focus more on et rather than HP numbers.
HP numbers don't mean all that much, it's who wins that counts. From that standpoint I would suggest a 3.73 ratio rear gearset as a great mod to wake up your '85, along with the pulleys, exhaust, intake and carb work.

Unfortunately, your '85 has the weak 7.5" rear so I would think about just replacing the whole rear with one from a later model Mustang and do the ring and pinion, seals, bearings etc. at that time.

If you're really set on having a dyno readout of 300 HP, you'll need better heads, at least, plus the other items mentioned.