Best option would be do your development with the 1.0 unit ( as you already have it ) and if it works just buy a decent 1.3 unit and fit that , if you get into rebuilding Nissan or other Japanese engines you will really get into money and there are lots of s/h units around for reasonable money , The only question I would ask is WHY
I have driven lots of engine swapped minis over the years and I have not found one that worked well , always something wrong ie weight distribution , driveshaft angles , cooling problems etc etc , I could understand people wanting to change units many years ago but since the introduction of the A+ 1.3 engines reliability of the mini unit has improved and a decent mini engine modified will be a much more balanced solution , I know many of the modern engine / box units ie Suzuki , Nissan etc etc will have the advantage of a 5 speed gearbox and 16 valves etc but I personally think the advantage is minimised by compromise . I have found a Mini with around 90/100 bhp is perhaps the best balanced and drivable option ,and still will pass NCT and is still insurable as its the original engine with mods rather than a swap .
G