Converting non-roller motor

theres some small machining, and roller cam which is about tripple the price of flat tappet hydraulic.

what currently is in your 94 GT?

You can get the drop-in kits, but total they are something like $500-700. After owning a flat tappet 298 and then a roller 5.0(which I assembled), I dont think I would go to the trouble of converting. You could just about rebuild a roller shortblock for the same price as a conversion. 5.0 shelf cams usually start at $140, stock lifters are the least expensive at ~$120, you'll need a steel distributor gear and possibly custom pushrods.

And if you didnt know already, all '87+ 5.0 Mustangs came with roller cams.