[Moppie]

Yeah you will deffinitly good gains from an exhasut upgrade.

3inch from down pipe to tip should be pretty good.
It will cost the most, but give the best gains.

The intake is a tricky one with out seeing the stock system.
But it could make you 5hp maybe, and combined with an exhasut you might see maybe 10hp at peak. The 280 is an old design, and as a general rule the older the car the more gains you get from simple bolt on mods.