Don't know what to look for.. it makes the noise with no load forward or reverse, don't feel anything loose, brakes work fine, never tried applying brakes under power for any length of time to see if clanking..
RK 55HC,ym1700, NH7610S, Ford 8N, 2N, NAA, 660, 850 x2, 541, 950, 941D, 951, 2000, 3000, 4000, 4600, 5000, 740, IH 'C' 'H', CUB, John Deere 'B', allis 'G', case VAC
it almost doesn't have to be the brakes
a repetive clank like that makes me think of lugnuts first, then hub to axle nut and hub to axle fit itself. ford hubs of that era are soft cast iron and the axle is hardened. if the nut comes loose, the axle gets loose and wears.. usually the 50$ hub wears out first.. but after a while the more expensive axle will wear.. once the splines are worn you can't snug the nut up enough to keep the hub on the axle before the nut bottoms out on the axle threads.
lastly.. could be a wheel bearing.
brak clunk is usually a 1 time deal when going forward or reverse, followd by a lockup, squeal or constant drag.. not a repetative clunk-clunk-clunk.