Depending on where you live you should be able to find a really nice mid level bike used for the same price that you're going to spend for new rims and tires, and maybe new brake calipers if they can't adjust enough! Why go through that sort of expense for a bike worth $50? You're never going to be able to sell the bike with new wheels for what you paid to do that, no one is going to pay you $200 or more for that bike, it will be worth $50 with or without the new wheels. Forget it and move on, find a used bike and sell that Free Spirit, or give it to a neighbor kid.
Wag more, bark less
To convert your 1981 Free Spirit "Pinnacle" road bike to 700c wheels, first check your rear dropout spacing by measuring the distance between the two rear frame arms, it’s likely 120mm or 126mm, and you'll want to match the wheel's hub accordingly. Since 700c wheels are slightly larger, you’ll need to adjust the brakes down by about 4mm to ensure they align with the new wheels. Once you’ve picked the right wheels, make sure there’s enough clearance in the frame and fork for the larger size. Installing them is as simple as swapping out the old wheels, adjusting the brake calipers, and then test riding to make sure everything is aligned properly. If you're unsure about any steps, a local bike shop can help with the finer details.