Steel, 27" rims, stem shifters and stamped dropouts are indicative of entry level models with hi-tensile steel frames. The SunTour Honor rear derailleur and center-pull brakes (presumibly Dia-Compe) are also indicative of an entry level model. The most interesting component is the crankset, It's not the typical cottered steel crankset on the boom era models. While it is cotterless, it doesn't appear to be any of the standard aluminum models but a steel version. If so, this would place it post boom, probably very late 1970s to very early 1980s. That would be in agreement with a 12 speed.
The bicycle's manufacture was probably contracted by Marukin to a different company. The big clue is that the label states "designed by Marukin". Typically this indicates is was contract manufactured.
Serial numbers can be stamped just about anywhere on the frame. The most common locations are the bottom bracket shell, rear dropouts, lower section of the seat tube, seat lug and collars of the head lugs. If you find one, I may be able identify the manufacturer and exact year. Baring that, you could also check for date codes, which are usually stamped on the back sides of the major coponents. They can be identified and decrypted using the information on the components page of the Vintage -Trek webste. Component codes are usually not much farther than a year off of the actual manufacturing date.
As to value, there's not much there. Normally, I'd place this in the $75-$100 range but the large size does typically knock down the price. I think you are looking at $50-$75 in an average market.
Last edited by T-Mar; 03-28-13 at 06:06 AM.