Ok. Do some close research on the available Webers. The 28/36 seems most ideal to me. you might research sites like Redline Webers, they are a main importer of Weber carbs to the US. Need to think about choke type, linkage stuff, manifold adaptor, ect. There is likely an importer of Webers for SA, I'd look for that. Then there is jetting- the company in Oregon I bought from had jetting kits and recommendations on that too. The type I used is the 32/36 DGEV, with electric choke, it has been a great carb. The Subie's engine is 1.8L One other thing is a fuel pressure regulator, I used a cheaper one but it got a leak and I deleted it. Weber's are real sensitive to fuel pressure, I think it's recommended to limit to 2-3 lbs. pressure, there are Weber pressure regulators available.
Ron said the bits will cut iron, and they will, but at risk of shortened life. I sought out a tool shop where the single proprietor ( who had a huge shop w/ maybe 50 different work stations!) looked at my Gadgetman bit. With over 40 years experience, he had never seen anything like it--and remaking/fashioning bits was his specialty. I brought a high speed steel ball cutter I bought elsewhere to him, and he cut and modified it into a "hack" of the Real Thing for me. A very rough copy it was, I used it to do first stage Grooving on my stock Iron carb. throttle body for the Subie. Then finished up with the actual bit, all to preserve my real bit. IT worked, there was perceived improvement to the Subie. but nowhere as good as the Grooved DGEV 32/36 Weber. And the Weber has jets to tune it, the stock one not so. A big consideration w/ carbs, IMHO. The iron throttle body is common in Japanese carbs. I don't recommend using the Gadgetman bit in Iron, though it will do the job. Remember, Ron had access to new bits anytime! If you remove and examine the Primary bore of that stock carb, I bet you will find something that would compromise your Groove job on it. A funky vacuum port, or a big screw recessed into a cavity next to the bore, that limits your Groove's width. And how to re-jet it...?
So you have Aaron's Ignition Secrets download? Wow, you are a Gadgetman in more ways than one!
IF the Nissan's ignition is a magnetic trigger type, there are still plenty of upgrades that are possible without going all the way to Plasma. I know a great trick for MAgnetic trigger distrubitors, involving replacing the factory Brain, or Ignitor, with a GM HEI module. The HEI module is most always better than any stock Japanese one, and at least over here, readily available. IT does need mounted on a good heat sink, the wiring is easy. I can give detail if needed.
Hypothetically, the cheapest MSD Ignition box, the Streetfire, could be added at some point if desired, that would improve it a lot. You could fit High performance low resistance plug wires, premium cap/rotor (if available). Re-gap the spark plugs, of course. Maybe a better coil. Just using really good quality basic pieces can make quite a difference, it helps in lots of situations, cold starts, smoother running, cleaner emissions, elimination of misfires, etc., etc. Plus I found when I used top notch parts, tuneups last for Years and tens of thousands of mikes. A car I drove up to Reno last November from Phoenix AZ,(almost 800 miles) was given such a tuneup by me in the early Nineties, over 20 yrs ago. The owner, a good friend,claims it still has the same ignition parts I installed, and it has gone probably 50K miles or more. Back then I worked out of my home garage as a mechanic, and did many tuneups and carb rebuilds. I don't think I ever had anyone return for any more ignition stuff besides new plugs after I did a major tuneup. The most bang for the buck is the plug re-gap, assuming the Ignition is in good shape. As Dr. Jacobs said in his book--" Your Ignition can't be too Good!"
So, Yeah, I recommend a Grooved Weber, and at least Ohm out the plug wires, and re-gap plugs. That will really wake the old Girl up!
Tracy G