i believe you can fit the s2 rst lsd into the ib5 box but i could be mistaken. clutch would probably be an upgraded fiesta turbo one? you can use the cvh efi flywheel with the bolt holes enlarged, or use a 1.8 zetec one and i think the clutch may fit directly onto it.

keeping the silver top head would be more of a ballache than it's worth. the st170 valve springs won't fit it as the cotters on the silvertop are single groove and a different angle to the 3 groove ones of the blacktop and st170. The timing belt tensioner setup is also different. The silvertop sump and windage tray can work but you may need modified bolts or spacers to hold the tray at the correct distance from the crank. the inlet gasket may also not seal on the silvertop due to the port shape being slightly different. your best bet is to just get a blacktop head as they're cheap and much easier to fit!

hope that answers most of it