Untherneath the rearseat the MK2/3 have a more flat surface(hmm doubting MK2 1.4 now...), so a 360tank fits underneath the body. MK1 1.4's gets deeper near the side. Ive only seen one B19 MK1. But didn't look to close. This week i'll see one probably (maybe even buy it) . So im going to check that.
because its a 6mm return and 8mm feed, you need to at least change the intank set up to allow those outputs. or use an inside based alloy fuel tank etc
if your using a swirl pot, couldnt you use the standard pump to just supply the pot from the main tank, then use a clio pump or similar to supply the injectors? providing the you have a swirl pot that has the correct size connection for the different diameter hoses of course?