If you mean Concord Selecta 12, teh googles show that to be a lower-midrange bike, and likely suitable for a big clyde to start becoming a somewhat smaller clyde on.

The frame can handle you (if it's big enough, as Rudi mentions above), but the key would be making sure you have a robust wheelset on it. Usually this means just about any 36-spoke (or 40-spoke touring) wheelset and quality tires, not too skinny. Preferably 32mm (or if it has 27" wheels, "27 x 1 1/4." The wheelset it came with should be fine as long as it's true and round and with alloy rims, not steel. Wouldn't hurt to have someone who knows what they're doing check the wheel set for proper spoke tension. Modern double-wall alloy rims are preferable to old single-wall rims. If your bike is original from the early 80's, it likely has the latter.

If it's too small, or has steel rims, I'd give it a pass and just look for something better; much cheaper to find a decent used bike complete than to pick up something cheap (or free) and start the nickle-and-dime-and-benjamins upgrading.