A Holmes 500, will be the largest unit you can put on a one ton, but it won't be period correct. Neither will a 440. A Holmes 400(4 ton), 460(6 ton), & 470(8 ton),with "Platform style" service body, will be period correct, for a, '60, or '61 model 1 ton truck. Check out my wreckers here,
http://community.webshots.com/user/snubnose4754 , The Holmes 600(16 ton) wreckers I have, are the Platform style service body. My Holmes 525's(12 ton), & Holmes W45(20 ton), are the old style "Chariot" service bodies(pre1956).