Welcome to the forums. The OP's Excalibur is essentially a rebranded Bridgestone Superlight, manufactured using their Technart process, whereby aluminum lugs are die cast over tubes with slightly flared (and plugged) ends. This method eliminated the need for skilled brazers, reducing costs. It also allowed the joining if dissimilar and difficult to weld or braze materials. In this case, the main tubes and stays are aluminum but the fork is steel. The Technart process was also used for stainless steels and hi-tensile steels.

The components are typical of a mid-1970s, very low mid-range, Japanese manufactured model. The brakeset is the ubiquitous Dia-Compe centre-pull with safety levers. The derailleurs are the rugged, well performing SunTour VGT on the rear with a (reverse shifting) SunTour Compe V on the front and the desirable SunTour Power Shifters (I'm not sure if this last item is OEM, as the factory Superlights typically used stem mounted shift levers). The crankset is a cotterless, aluminum, swaged, Sakae Royal. All these items are typical of Japanese upper entry level models of the era but what elevates it a notch are the wheels, particularly the aluminum rims. One cost concession is the use of a nutted axle on the rear Sunshine hub, as opposed to the quick release seen on the front wheel. The saddles were typically a plastic base, padded vinyl Kashimax, as opposed to the leather saddle shown.

Despite the extensive use of aluminum (and in the case of the Bridgestone version, the Superlight model name), these were not very light bicycles. Claimed weight for the 23" model was 28.5 lbs. Original MSRP circa 1975 would have been around the equivalent of $180 US, as that was the Superlight pricing.