Would a red zebco 606 freshwater combo with 25 lb test Berkley trilene big game solar collector work well for big flatheads ?

Depends on how big of a flatty...

If it straps the gears out you can always hand line it

Don't know about the 606 but I landed a 31 lb flathead with an old Zebco 33 and 15 lb trilene caught in Denton creek when the water was up and flowing bank full.

Im sure it would work. Wouldn't be my first choice, and probably wont be the longest lasting rig for the job.

Zebco 808 should do the trick.
I have been pondering the idea of getting 1 Zebco 33 to go along with my ABU C3s. C3s are all i use, but when i was a kid 33s was all i had. ive been wanting to get 1 to see if i could catch a monster cat on 1.

Give it a go and get pictures!! then give us a report..

You may want to pull line to check to see if the drag is set and not seized up, you'll need a good working drag.

That's a fault I've seen in them just getting into some nice channel cats.

They don't make them like the used to. I've thrown away a half-dozen Zebcos in the last few years just from sheer frustration over the poor build quality. Gears are all plastic and pot metal now, even in the 33 classics that still have the stamped metal housings. I keep a couple for my kiddos when we fish channel cat and panfish, but I've had 2-3 lb fish peel drag off of Zebcos with little effort. Not sure about the big boys since I get the small reels, but if the small reels are indicative of quality, it might be rough.

Not consistently. You'll be very upset if you lose a big fish due to sub-par gear. At least I would.