Those brake lever extensions aren't really "interupter" levers. They were called "safety levers" at the time but were actually unsafe as the levers flexed too much for hard braking. They can be removed from your existing levers if you can find the shorter red push-through rods to replace the longer rods of the safety levers, and then you could add rubber hoods. Or you can remove just the lever extension and leave the longer rod sticking out of the brake lever. This type of lever with cable coming out the top only applies good braking force from the drops. Simpler and safer to replace the whole levers if you want to ride on the hoods and brake from there.
The steel cottered 3-arm spider crankset is very low end. You may have trouble removing the cotter pins to replace the crankset. You'd have trouble finding a replacement rear wheel for this as it's probably got 120 mm axle spacing (if it takes a 5-speed freewheel). I agree with Laura that this bike isn't worth a big investment, but you could get some enjoyable miles out of it.
Oil is good, grease is better.
2007 Peter Mooney w/S&S couplers/Terry Butterfly
1993 Bridgestone MB-3/Avocet O2 Air 40W
1980 Columbus Frame with 1970 Campy parts
1954 Raleigh 3-speed/Brooks B72