I have that Centurias MLP...great cover and their hard rocking metal of old definately delivers the feeling! I've never checked out Ninja because the cover is goofy as hell, suppose I need to change that.
I love that Excalibur demo LP on Dies Irae. I think it was the first S.A. Heavy Metal record I ever heard and it still is a favorite. There was something unique in their sound, probably because only that guy from the UK had a metal background...
I've just remembered when this was advertised as a "recently discovered brazilian private metal LP from 1984" on ebay and people bid over 100$ on it...I think this was even discussed here, probably in the ebay madness thread.