Both 20Vs, irrespective of their 'top' colors, were built from the factory to run on 100 RON. Which means they will generate 160 or 165 hp on that kind of fuel. Our 'super' is graded at a mere 90 RON and high octane is claimed as 95 RON, which in both cases is pretty much optimistic. 87 and 92 would be a more realistic rating for both 'super' and 'high octane' respectively, here in Pakistan.
Sure you can make the 20v's not knock on 'super' by retarding the distributor into the negative range. But then again think about the actual horsepower figures you'll be generating on 87 RON. Pretty much somewhere around 120-125hp. Wouldnt it be much more feasible to swap in a 4A/7A instead if you did want to run on 'super' in the first place and save yourself the hassle and have a more economical and reliable setup as well.
We swapped a 20V BT in a friends 2-door Starlet and J18A in a friends 4-door Khyber a few years ago. Both were running on high octane and were tested a couple of times in a short drag and the Khyber was atleast a couple of cars ahead in both runs. The J18A Khyber's octane requirement was 89 RON, produces a 135PS stock, and was 2 doors heavier. You do the math.
And any car on CNG will not knock unless its running compression ratios in the 14s or something since its octane rating is 125-130.