The hardest part to find might be the flywheel for the 350 Buick engine. Years ago I swapped a 350 into a Jeep pickup and found that to be a rare item. Might now be available from modified (Hot Rod) sources. Check V8Buick forum. Mr. Ed
I saw you post this on the JCCA. I was going to suggest the 350-T18-20 combo but it seems you've already considered that. Ten years ago I looked at a J-truck with that exact combo. The guy was selling it for like $500. It seemed like J-trucks and FSJ's were everywhere and cheap. Now, I can't remember the last time I saw one at the pic and pull.
You could do a rebuild on the 225. It is a torque monster and will put out good HP numbers with the typical big three upgrades.
It can be mated to a modified Ford T18 or you can get an adapter kit.
You also have the option of installing an SM transmission.
The T18-D20 combo from a J-truck or Wagoneer will be problematic in a C101. As well as being scarce, they either have a goofy long bellhousing and long input shaft, or a standard BOP bell and a 5" thick adapter, along with a 12-13" long input shaft. It's a very odd setup.
If you want, you can convert the Jeep T-18 to a short shaft (6" Ford T-18 input shaft kit, ca $200 from Parts Mike), and then use a regular BOP bell. IMO there's really no reason to seek out the 350-T18-D20 combo for this conversion, since you will have to convert it anyway. The only advantage will be that you can use the existing 225 frame towers for the 350.
The neat swap for a Buick 350 is in a TH400 equipped C101... but the 350 is too much motor for the 3-speed T-14 (the 225 is too much motor for the T-14, IMO).
If you want a truck 4-speed, any of the T18/NP435/SM420/SM465 will work if you are willing to buy an adapter kit. Read the Novak site. http://www.novak-adapt.com/ You can use a Buick 350 if you can find a flywheel. The small block Buicks 300/340/350 will drop on to the 225 mounts, but you'll have to move the radiator forward.
Personally I would go with a SBC and modify the mounts. Or keep the 225 ... they are fine motors. The Buick V8s are great motors, but there's no drop-in for these in the C101, except for the TH400 equipped cars.
I believe that the Buick 350, although rarer, is a better motor for the application, lighter (125 lbs lighter than a sbc!), and produces good TQ. The aftermarket roller chain and external oil pump upgrades have solved most of the problems the Buick V8 ever had...
Besides - it is also a "Dauntless" motor.
Thanks for the info about the Gladiator combos. Looks like a 350/SM465/D20 or 350/T18a/D20 will be the ticket. Now to find a pesky 350 Buick flywheel...
1969 Jeepster Commando w/Buick 231. T14/D20. D30/D44, 4.10 Locked/Spooled. 4x disc brakes, Saginaw PS. 32" x 9.5" Super Swampers.
1970 Jeepster Commando, in pieces. Buick 350 / SM 465 / D20.
True, the Buick is a great choice, if you can find one. They are light and they have a lot of torque for their displacement. But they will be harder to source than a SBC and they will be more expensive to rebuild or repair. Certainly the Buick outclasses the Gen I 350 Chevys from its era. However, I would guess that a Gen II with aluminum heads or the aluminum block Gen III will be as light or lighter than the Buick, and with its native EFI make as much power and torque as the 40 year old Buicks. With better economy.