Don't know anything about the company but if there's enough travel in the wheels you can probably fit a 64 1/2 '' blade on it. If it's old and beat up, the built-on tension gauge probably isn't all that accurate whether or not you have the length right. A blade doesn't need to be fully tensioned for the bandsaw to work, you will probably be alright eyeballing it, just take some practice cuts to make sure the blade isn't popping off and it's cutting straight. Make sure you get the blade thickness right- it's probably standard as well but some saws can only take one size.
If you want to get the tension right and don't want to buy an expensive gauge, it's not hard to do with just a good pair of calipers. Find a pair of small objects that you can clamp securely to the blade (without damaging it) and measure accurately off of. Something as simple as a pair of socket cap screws with nuts might work, measuring off outside of the caps. Raise the guard, untension the blade, and clamp them 3 inches apart. Measure the distance exactly with the calipers- then tension the blade. You want a strain of about 2/3 of a thousandths for every inch for a normal carbon steel blade- or 0.002'' of extension over 3 inches.