Well, you get your torque from quickly opening and closing valves, and thus moving air quickly into and out of the engine. I would say that you would want a high torque cam and a stroker crank with moderate sized pistons. The godfather used to say that stroking an engine did more than just upsizing the piston diameter.

I think the real trick to building a high performance motor is getting the carbs and the exhaust matched to the air pump (the engine). You have to have all of it breathing correctly and it has to do with ratios and back pressure. I'm not an expert at that and I don't readily have a guy to direct you towards. I will caution you against reading 10 different builds and seeing that one guy had good luck with this cam, and another with that exhaust and another with that carb and then trying to piece 10 builds into one. You'll end up selling you project not running and asking too much for it (look around- it happens- a lot)! If you want to do it, find someone who knows high performance engines and buy everything through them or have them deliver a turn key engine. The moment you save $20 on a part is the moment their warranty or advice is done.

Just my $.02.

I don't know much about building high torque engines either.  What I do know is that it's complicated and like Nick was saying . . . it's a SYSTEM, not a bunch of random components pieced together.  I've ran a bone stock 1600 single port in a 73 bus.  I've run a bone stock 1600 dual port in the same bus.  The single port has a smaller carb and intake, but it has noticeably more torque on the bottom end.  The dual port with it's less restrictive intake and bigger carb has more power on the top end, but a single port will still beat it off the line.  Why?  I have no idea . . .

Speaking of single ports in a bus, the Godfather used to always tell me that if I really wanted to wake up a single port, add ratio rockers.  He said "they love lift, but they hate duration."

So, my 0.02 cents worth (which isn't worth a penny after taxes) is the same as Nick's.  Do your homework and find a design that will deliver what you are wanting and don't skimp.