Porter manual shows front and rear ARBs on Mk1 Punto. Whether on all variants, GOK. But if there's a rear one, I can't see them not fitting a front one (oversteer city?).
Rear one will run in parallel to the rear torsion bar.
front as fingers says should join to each side wishbone, i think you would be able to drop a gearbox without touching it as for the struts I'm not sure (the ARB would make life more difficult anyway)
are you 100% sure? the only cars i've known not to have them (built since the 80s) have all been large 4x4s which need huge amounts of axle articulation for off road use.
I had an 86 coil sprung LandRover without anti roll bars and just going round a roundabout was a pretty scary feat
The smaller -- well, sub 1108, Cinqs din't have ARBs, nor do some Nobles, but that pretty much wraps it up for road going 2 wheel drive stuff of recent vintage I think.
I have a '97 55sx and that doesn't have anti roll bars front or rear, as was mentioned above I think the earlier low spec ones don't have them. I also thought about adding them as it does have a tendency to feel very soft in corners. Need to get it running again first though.