Mine are made of aluminium with stainless steel plate against A-arm.
Much more complex design.
Those things you show there is going to break or bend under extra power from big engine. Ok for a sunday driver thoug.
Cost efficent? No not if you count your work hours.
but if you have acces to milling machine and lots of spare time, yes it is.
Mine look like this:
http://v-dubs.no/haraune/album12/photos/photo_15.html