mr. singh will be able to comment on the engine as he has a manual SB3 though it is a standard 1.5 with a different camshaft + map applied (although I could be wrong here).
different cams and map, yes, although in addition to map and cams are the valve springs and exhaust.
i cant really comment on the 1.3 engine as i went from a 1.1 to my SB3. the only reason i changed was the SB3 had more toys and it had the engine, the 1.5 i wanted in the first place, the SB3 kit being a bonus.
the SB3 will use the normal 1.5 parts, i can confirm that the clutch is the same on both and so are the service items, ALTHOUGH the valve clearances will requires checking and adjusting every 30,000 miles or 3 years over the 60,000 miles and 6 years.
the SB3 does shift but id go and drive it and compare it you your 1.3 and see which one you prefer.