Hmm... Macintosh fun times or active outdoor pursuit? Why not both!
The concept is very simple as you can see, just get the trucks off any old skateboard, drill holes in the bottom of your G4 case and bolt them on. There are a couple of issues along the way though...
The G4 case alone is a hefty old thing, so to keep as much weight off those tiny wheels as possible we got rid of everything we could from the Mac's insides, leaving only the metal frames under the drive-bay and power-supply for total rigidity.
This [above] was the obvious place to mount the trucks in order to keep the base of each truck within the length of the case-bottom. This is the strongest way, but the high centre of gravity is a pain in the ass and with such a short wheelbase the Mac is prone to tipping forwards and backwards. For any sort of stability at speed the trucks-axles need to be extended over the edge of the case-bottom, pictured below.
The two bolts at the back weren't going to be enough, so to keep the trucks as stable as possible with them over the case edge we drilled an extra set of holes in each truck, about an inch along from the original rear holes, pictured below. Bunching the bolts together on the inner half of the truck isn't the strongest method, but it's the best you can hope for if you're after a long enough wheelbase.
Welding the trucks on in this way would be ideal, but there is also the problem of case flex. We initially bolted the trucks straight on to the case-floor, with only the plastic spacers from the skateboard on the inside and we noticed the bottom of the Mac was bending around the bolt holes after just a short test. Spacers under the case is out of the question because the Mac rides a little too high as it is. As a quick-fix solution we added two plywood inserts on the inside of the case-floor to give the bolts some extra depth and provide a little bit of suspension-damping, pictured below. This seems to be holding up superbly to the knocks and bangs for now, but I'm sure there's a far better way to mount the trucks for maximum shock-resistance in future.
Read more in this post - Skate Mac Redesign
Ride responsibly!