I'm not familiar with the Cubs. You might want to post something on the Cub forum to get more answers.
Before you put a lot of money into beefing up a GT for a loader, you might want to just shop around for a smaller (preferably 4WD), older gear-drive CUT that already has a loader.
The Case-Ingersoll 644,646 & 648 close to being a CUT in their own right. The one that was on ebay went for $2400. You'll probably end up with more than that into the purchase, front-end upgrade, and hydraulic parts (hoses, cylinders, valves etc).
Some models that I've seen with loaders in the $2-4k price range:
Yanmar 135
Yanmar 155
Kubota B5100
Kubota B6100
Kubota B7100
Mitsubish MT372
There was just a Kubota B6100 on eBay (in NY, I think) with a loader AND BACK HOE that had a buy-it-now of $4500. It sold quickly.
You stated that you don't have the money for the loader project right now, so maybe just pickup a heavy GT that has a 3PH and do the other stuff you mentioned with that, and then keep an eye out for a small CUT w/ a loader later.
If you are patient, I've seen 2WD smaller CUTS (like the B6100E) w/o loader go for $1500-$1800.
If you want to build your own loader, that is great (I wish I had the fabrication skills), but you'd be much better off doing it on a small CUT than a GT, as you'll be much more likely to have a front axle that can handle it, and an overall weight that is more likely to handle that load safely. Plus, with all the models above, and most all small CUTS, you'll get a long-lasting, smooth running, fuel efficient 2 or 3 cylinder liquid-cooled diesel engine, instead of a 1 or 2 cyl (usually) air-cooled engine (that are usually louder than the diesels).
Plus, if, down the road, you want to sell said machine to upgrade, you'll get your money back out of the CUT. The Cub 782D (has a 15HP Kubota Diesel engine) that had a loader on it on ebay has gone unsold at a price of $5k lately. It is a beautiful, well-done machine, but the bottom line, is, for that price, you can find one of the models listed above with 4WD and a loader almost any day of the week.
Just some more things to consider. All that said, of the GT's that I've looked at, the Case-Ingersoll 4xx, 40xx, 6xx, and 60xx series tractors look like the best GT candidates for your loader project.