how i missed this question..
i have a special thread about it ,. bikes labelled 78cc are not 78cc they are 85-88cc.. i have measured up..
they have same bore i.e 47mm as honda cd 70 therefore same piston can be used in both.. but 78cc have very long stroke 49mm same as cd100,cg125 whereas honda cd 70 has 41.5mm...
now regarding parts ..carb is samebut its jets are different along with needle etc.. in short carb is different..
both have different cylinder block,,,
rest the crankcase and clutch etc are same..