What is safer on the street? A 3 point belt, or a 5/6 point harness with roll bar?

With the extra hassle and confinement of the 5/6 pt harness are you going to wear it faithfully and everytime you drive no matter how short the drive is? A big deciding factor would be can you actually have a proper 3pt belt in the car. Early A's don't have the upper anchor for the belt so you would have to add it. The cage and harness are likely much safer, but I would go with sebring seats with 3pt in mine. Something like this is what I would install, usually you can find them for around $350-400 on ebay.
http://www.ebay.com/itm/96-06-Chrys...pt=Motors_Car_Truck_Parts_Accessories&vxp=mtr