My 1983 miyata 610 has 120mm spacing, so if you want to put wheels with a 130mm or even 135mm axle in there, you will have spread the hell out of it. You need to find this out, and that is why I specifically asked for you to tell us what components your bike currently has.
If you're going to make any changes, it's cheaper and easier in my opinion to just get a 5 spd or ultra-spaced 6 speed freewheel if bigger range is your goal... it's only a one-part swap. I thought I wanted 700c wheels too when I got my bike, but there's really nothing wrong with the older wheels IMO.