Rice bran is 22% healthy fat, provides cool energy and is cal:phos balanced as long as you buy EQUINE rice bran. Tractor Supply sells Manna Pro's "Max-E-Glo".
Just wanted to point out that not all rice bran is fortified just because it's marketed as equine. I feed my horse "Equine Shine" rice bran, which is stabilized, but not fortified. I guess I should also comment that it's very important to get stabilized rice bran, as otherwise it goes rancid very quickly, possibly before you even get it home depending on your feed store (the one time I checked the non-stabilized brand at my feed store it had already been on the shelf 2 months
I'm OK with feeding my horse non-fortified because I'm only feeding 1/2 lb a day and I've balanced his diet using FeedXL.com
(which I highly recommend).
Beet pulp and rice bran are great for putting on weight, as is the alfalfa you're already feeding. I'd also add in a ration balancer or vit/min supplement, as it's pretty much impossible for horses to get the nutrients they need out of a block.
I'd avoid Triple Crown Complete for your guy- it's high in sugar (not good for ulcers). If you want to stay grain free, I'd recommend Triple Crown 30% Supplement
(plus beet pulp and rice bran for added calories) or Triple Crown Senior
. Both are very low in sugar/starch.
Continue to give him as much hay as he'll eat- you can put the grass hay into a hay net to prevent waste and then just give him the alfalfa outside the net (unless he's wasting the alfalfa too, but most horses I know won't leave a scrap of alfalfa behind
) Having small amounts of food constantly going through a horse's system is about the best thing you can do for them, particularly those prone to ulcers.