I'm not sure, I wouldn't have thought so though as they are different.
Why not save up for a bigger engine? Say a 1.4 or 1.6 sport conversion. It's quite a simple engine conversion to do.
Changing manifolds and injectors on the 1.2 will have no possitive effect whatsoever tbh.
Id let somebody else do it if i was you, im not tryin to affend you but u dont exactly sound the most mechanically minded, spi stands for single point injection by the way, not the trim level!!
You wont need a Gsi ECU as, well its not a Gsi but standard ECU would need looking at because of the new injectors etc. The manifolds may not fit because of thee size of the ports, but i dont know because iv never tried or seen somebody do it.