if you are going to race this car at all, i would leave the roll bar in. if you are going to restomod the car instead of restore it to original condition, and relegate the car to street use only, then perhaps lose the roll bar.
restoration parts are pretty much available from any mustang parts supplier, like virginia classic mustang, autokrafters, national parts depot, dallas mustang parts, etc. if you want recommendations on building the car for the street or track, decide first exactly what your plans are for the car, then tell us and you will get a ton of recommendations.