[dsraven]

it would be kinda hard to make a universal fit splash gaurd due to differences in axle center line and other factors but if you wanted to build a steel one yourself you should likely put the suspension through a complete cycle upwards to ensure the existing hole is not going to contact the moving parts. then build the gaurd around that and make it removeable in case you need to do control arm bushings or other front end work at some point in the future. some studs welded onto the part could have nuts on the back side of the inner fender to secure the panel and then nobody sees the fasteners or if you don't mind seeing the screw heads you could use rivet nuts on the inner fender and fasten it down that way. a strip of foam tape would work as a gasket. build a pattern from posterboard and use tape to put the parts together in mock up.
my inner fenders have a huge hole due to the strut type suspension with upper and lower control arms. I will be changing the struts so when I get to that job I will remove the strut and put the suspension all the way up and see how I can make a bubble to cover the hole. I'm with you on the splash thing, I hate a dirty engine.