Chris, I have mounted my speakers below the dash factory style. The factory use Pioneer speakers, plus a plastic spacer that fits between the speaker & the dash. I bought Pioneer speakers from a hi-fi shop & the spacers (also made by Pioneer). Unfortunately the spacers & speakers were not compatible, the preformed holes didn't line up & I couldn't modifiy them as the spacer holes are on lugs.
What I did was use a sheet of MDF the same thickness as the spacers, used the spacer as a template & cut out two doughnut shapes, drilled to match the speaker hole positions & sprayed them matt black.
Then all you need to do is offer up the spacer ring, mark your positions on the dash, drill a couple of starter holes & jigsaw them out. Be careful as there is wiring for the wiper motor behind there. I removed one side of the dash to cut, but the other I had to cut in place 'cause I couldn't remove it.
All finished it's almost impossible to tell mine from a factory install. But the beauty of making your own spacers is you can fit larger speakers if you wish.
All in all it's a reasonably easy job, the hardest part is cutting out the holes in the dash., if you don't rush it though it's no problem.
Sniff my Diff ;)