The SRM range for Saison is 5-14 - there ain't no way you're getting anywhere near 14 with 70/30 pils/munich.
and besides, AFAIK, a saison is in the same color range as the dort, so if its good for one, its good for both. - dorty shouldn't really be much higher than 6 - should have a nice rich gold color like this:
- (pic kinda sux since it was with my old camera).
as far as how to do it - I was under the assumption that you were shooting for mid/high 50s on both, which would mean just an even split of the whole deal (first and sparge runnings). if not, you'll have to do a little math and figure what percent of first runnings and what percent of sparge you'll need in each kettle to hit your preboil gravities. if you don't have one, this is where a refractometer would be really, really helpful.
however, now that I think about it, you're adding sugar and the wheat runnings, so if you target 1.056, you'll have no problem getting well into the high 60s on the saison if you just evenly split it.