Castell y Gwynt, Y Glyderau 1
Image by thesweetcheat

That sounds like a plan.

Book says this about your "up" route:

"Pleasant walking up a gentle ridge to join the ordinary route up Glyder Fach at half height. Superb views of Tryfan's east face."

Superb, still a bit drizzly here at the mo, but it WILL clear up a bit, not too much though i hope, you can have too much blue sky, cant you ?