The formula for calculated a horse's weight is:
Hearthgirth X Hearthgirth X Body length (in inches) divide by 330.
Hearthgirth is measured about 4 inches behind the front leg.
Body length is from the point of the shoulder in a straight line to the butt.
I tried the formula on one horse that I have resently weighed.
8 year old Percheron G 16.1. Based on the formula he should weigh 1367#, he weighs 1355#!
Tried it on another. 22 year old Percheron G, 17.1, on the thin side or he can't move 1610#. Sounds about right.
If your vet doesn't work on many drafts, don't rely on them to guesstimate his weight. Most are way too generous. If the vet is trying to figure out doseage on say sedation, he will over dose him. Drafts are typically very sensitive to sedation. Keep that in mind.
The Cleveland Pellets. Don't discount the quality of the product a small local feed mill can put out. It's probably an alfalfa or BP based pellet (12% protein), 25% fiber and added vitamins and minerals to make it a complete feed. You're also supporting your local farmers and not wasting money on slick magazine ads. Wet it down and you have the mash you're looking for.