Unless he has an extremly large or small head a halter for an 800 lb. horse will most likely fit fine. If he has a smaller head you can try an Arabian size or a Cob size. The Arabian may have narrower straps so you may like the look of the Cob size better.
A quarter horse.
halter traing is ground work, and teaching a young horse to lead on a halter.
As a child I actually saw this horse. Along with the Buckskin and black and white Pinto ridden by Lorne Green and Michael Landon. As much as my research has been able to turn up the black horse was Quarter Horse or a Quarter cross. But this question deserves more research.
Gene Autry's horse was a morgan/quarter horse. Roy Rogers horse is a Quarter Horse/Tennessee Walking Horse.
Appendix.
a Morgan is a breed of horse and a welsh is a breed of pony... Morgan x welsh horse simply means that it is a cross bred horse and the two breeds that it has in it are Morgan and welsh
The D shaped, metal ring on the side of a horse's halter.
The most famous Quarterhorse halter horse is probably "Impressive"
The Azteca is a cross between a Quarter Horse and an Andalusian.
The cross between an Arabian and Quarter Horse is not actually a breed. This cross is more commonly refered to as a Quar-ab and although the AQHA (quarter horse registry) will not accept this cross in their registry, the Arabian registry will accept this in the half Arab registry. This means you can show your horse at Arabian shows in the half Arab classes. The Quar-ab is a very pretty horse. You get the beauty of the Arabian and the calm nature of the Quarter Horse.
Perhaps the American Quarter Horse, especially those bred for halter would be the dream of a body builder, if of course, their idea of beauty is an extremely muscular horse.
Training a horse to lead when he has a halter on.