Another guy ask the same question on a French Forum a while ago. I have save the topic on my hard drive because I found there was interesting things in.
Here is a translation.
1 step. Use 24 choke in a 28pci carb with an air horn. Glasspack exhaust and 010 dizzy. 7.5 cr. Engine will be more funny and have a nice old speed-cal look.
2 step. Ported and polished heads, angle valves job and 1.1 rockers from 1300-1600 engine and -3° to the stock camshaft. I think it was how they modify Formula vee engine back in the days.
3 step. VZ14 cam and 1.1 rockers but you have to notch the pistons to prevent valves hit them. 31pict carbs and 8.1cr.
4step; webcam 218/119 cam, ported 1300 dual port heads, cb hi-flow manifold with 34 pict and air horn.
5step; webcam 110/119 1.1 rockers, ported and polished heads, radius angle valve job, stainless steel valves, 9.1 cr, you also have to notch the top of pistons, HD single springs with hd alu pushrods, lightened Bilstein lifters, dual carbs.
Some funny things to do on a 1200cc. But it will cost you less money and work to put kadrons and an exhaust on a stock 1600.