Bob,
I don't know anything about using the 108 sub-frame mounts, but it does sound like an easy way to raise the front a bit as long as you're at it. Assuming they otherwise fit well, the question is whether 6 mm is enough. If it's not, you've still got a lot of work to do to raise it further, and if you have to do that work anyway, then I'd go with the 113 mounts. As James mentioned, I paid maybe $100, too, though I know prices in Australia are much higher.
When I got the rear of my car about right, the front was then very low, so I raised it about an inch by adding 1/2 inch spacers on top of the springs, a la Jim Villers. It still sits a bit low in the front, but levels out nicely with a full trunk, and I like it that way.
Good luck with all of it!
George Davis
'69 280 SL Euro manual