Apart from the open deck versions of the engine block that were used in the early V4 years there is not much difference between blocks, if any. When you go tuning you need a closed deck version, which your engine will be if it is from the same model year as the car. With the supersats you already have some of the goodies that makes the engine stronger than standard. I believe the camshaft is not stock either in that setup. Is it a 7.2? Of course you can opt for a 7.6 but the question is if you’ll be having much fun with the old-women speed limits in lille Norge. I know someone who ownes a Sonett with a highly tuned engine with a 7.6 cam and he says it is a blast to drive, but it is a bit of an on-off affair.
As the old saying goes: speed costs money, how fast do you want to go? Of course you can start with having the block bored up to 93 or 94mm, but you need porting of the heads and inlet manifold as well, complemented with bigger valves; the engine needs breathing. If you go for stiffer valve springs you need metal gearwheels; the standard fibre wheels do not like high revving, nor high loads as a result of stiffer springs. A high flow oil pump would do nicely. I don’t know much about Solex 2 port carbs, but the general consensus is that once they start to wear out the best thing is to replace them. I wouldn’t bet on them if I wanted to go over 100hp. Go for either Weber 32/36 DGV, 36/36 DCD or 40 DFI. If you really want something special, opt for a special manifold for either a single Weber DCNF or two. Last but not least, update ignition, it is the easiest power gain to get. If you haven’t got rid of old fashioned points, start there and convert to Pertronix or similar. When you really want a boost go for something modern that can be programmed, like Megajolt, 123 or Nodiz. If you search for Megajolt in the project section you may find the thread with the links to my Megajolt conversion.
This was only a short overview of the first things that came to mind. Hopefully the experts with tuned engines will give their 2 öres.
'75 96; very long-term project
'83 99; after 12 years of use gone to donor heaven
'94 9000 Aero; after 12 years of use about to be donor
'02 9-5 Aero; daily family driver
'96 9000 Aero; pappa's daily driver