While I agree that MOL has nice views when you are at the lakeshore (including, if I recall correctly, the food prep area), I actually really liked spending two nights at GLH and when I did my Mokowanis/Belly backpack last summer -- mainly because my GLH campsite had it's own access to the lakeshore. I dayhiked to Margaret Lake one day and Stoney Indian Pass the next and found the extra distance wasn't significant, whereas the easy access to sunrise and sunset views on Glenns Lake was a real plus.
Spartan, you're going to find a lot to enjoy on your trip into Mokowanis.
One thing: I have no idea how experienced you and your dad are (you mentioned in another post that he was 66 and in good shape but "not a mountain goat"), but you if you didn't already know it, the hike up to Margaret is not on a maintained trail (although there were some cairns to follow when I was there) and involves a little scrambling up the cliffs. Also, depending on when you go, the vegetation can get quite tall and the creek is very noisy, so if you go, please be particularly bear aware.
If you do decide to switch out the GLH site, I would make sure you are clear that you want MOL not MOJ.
Have a great trip! And be sure to post a trip report for us when you get back!