well unless you happen to have a good 1.3 ex championship Ka engine laying about like i did (Recent LHD KA rally build on here) then yes its a good idea, but remember your budget, if your going to spend most of it on making a good chassis (cage, suspension, tyres) then your going to have to stick with the standard 1.3 just remember what your really going to need: not just engine, ECU and loom etc etc but ignition barrel for acceptable keys possibley!! all the little nuts and bolts etc etc. and if your incompetant doing it yourself how much is a reputable welder going to cost for the engine mounts etc etc
there is a 1.4 convert ka on pistonheads with full cage etc in it
good luck