What am I looking for?

Got a picture of a build in my head. But not sure what frame to search for.
I want a 700c frame with horizontal top tube. Rigid, obviously. But the twist is that I want to be able to put fat tyres in there. Not huge, but about 700 x 50.
Most old steel frames, which I have a few of, don't have enough clearance for such a tyre. Any ideas of the kind if thing I should look for?

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No they don’t you need one of those modern gravel bikes like the Rough Stuff Fellowship used years ago.

Modern! How very dare you!?

Might an older frame designed for 27" wheels work? Is the issue width or height clearance?

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Raleigh Pioneer, Marin Stinson, klein adept?

Diamond back something or other

Ridgeback thingy

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Singular Peregrine modern but classic

https://goo.gl/images/xhptkp

Ooh pretty!

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I have an aluminium trek 7900 multitrack frame, takes 700c wheels, would need to check what size tyres will fit. Takes cantis, 135mm rear dropout, geometry is more hybrid/flat bar road than mtb, but I guess anything that fits your description will be. Can be done for cheapish with stem, bars, seatpost, and a few other bits included. There's a thread with pics somewhere, in road for sale I think but I can't find it right now, let me know if interested

Edit: it's a trek size 22", I'm 6'1" and it's only just small enough! Don't know what size you're looking for

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50mm road tires are huge. I have a Miyata triple cross and I think it would top out around 42mm or 1.75 inches tire width without fenders.

I would think about a Soma Fog Cutter or the Pescadero frameset for super fat 700c tires. The nice thing about the Fog Cutter is that with disc brakes you can go to 650b tires and run super fat ones. Rawland makes a frame that can take super fat 700c rubber as well. Surly is the old stand by for gobs of tire clearance on steel road frames - still 50mm might be a bit much. Rivendel has some pretty good tire clearance on its frames - I believe the Atlantis might get you up to 50mm with fenders. But its a touring bikes so your looking at cantis or vbrakes. Check out the New Albion Privateer as well - its a real bargain and can take some fatter rubber.

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Foz,how much do you want for the frame?