Welcome to the forum.
I was glad to see a build with 4age in the title. But the 20r is a real powerhouse. I think that you should go for it. Umm, how much do you want for the 4age carbs.
Seriously, from a traditional point of view the 4age seems like a perfect fit and it seems to take a bit of abuse from time to time. I rebuilt one, had it in the frame for a lot of the work and then ended up buying a wiring harness that had a beat-up but running 4age attached. I put the old engine for doing the wiring work, then test starting the engine to see that everything worked, then a little run down the driveway and then, 7 years later it's still in the car. It's never had even a minor problem. My shiny rebuilt engine has yet to be used despite some enthusiastic driving from time to time.
As far as ground clearance goes I was a bit apprehensive about my minimal pan clearance. Sorry for the crappy photo but you can see the oil pan plug. The block of wood is 3 3/8" high. I was very cautious of speed bumps for quite awhile but I came to the conclusion that because the pan is just behind the front wheels, speed humps at least, aren't a problem. The front wheels go up and so does the pan. The only problem would be something like a rock but that's not too common on the roads that I drive on. I'll take my chances on that one. Putting the engine at that clearance let me have the hood line etc. that I wanted.
Some folks that start these projects just kind of fade away. But I think that a guy who crazy glues a gash back together and goes back to work on the car stands a pretty good chance of ending up with a fun car.
Good luck with decision.
Ron