I don't think the 50Mm will work. Its not going to matter how much you use, its the the fact that its only half the concentration you use... even if you were to use twice as much, the ph is the same.
As to how much BW to add before you pin, its kinda a personal thing... its mainly to take the burn out of the AA. No matter what dose if IGF I use, I always backfill with BW to at least .8cc's and shoot .4cc's bi-laterally in the muscle worked.
IGF may well be ok reconstituted with AA at 50Mm concentration... But I have always been told to use 100Mm.