Welcome aboard Freeman41, don't forget to post some progress pictures of your dad's Spyder.
As for the rear anti roll bar question, light weight and a very low centre of gravity mean rear roll isn't an issue in these cars. Phil J swears by a heavy duty
front anti roll bar though, which he says really improves front end grip. Mind you, his first Sammio started its life as a courier van which had a front anti roll bar the thickness of a bootlace. I'm going to run mine with its standard Vitesse suspension (albeit dramatically lowered and fitted with new dampers, polybushes, etc) for the time being and see how it fairs on the road. I can always retro fit alternatives later in its life. Good luck and I'm looking forward to seeing another build progressing.