A sure method of pinpointing the cause of low compression in an individual cylinder is to perform a leakdown test. This involves special equipment which applies compressed air to each cylinder through the spark plug holes. As the air leaks out of the cylinder, a gauge shows how fast it is leaking out. If the air is coming out the exhaust, you have a bad exhaust valve; if it's coming up through the carbs, bad intake valve, and if it's leaking into the crankcase (you can check by removing the oil cap and listening while the air leaks out) it's bad rings. How many miles does the engine have on it? If mileage is over 125,000 or so, valve job (and timing chain, etc.) time is at hand anyway. You can save a lot on a valve job if you remove and reinstall the head yourself, if you feel comfortable doing this. If you've never done it on an overhead cam engine before, you should enlist the help of someone who has, along with your Haynes manual. If the rest of the car is rust free and in good condition, and if you like the car, it would be worth it to do the valve job (if needed) AND put the Webers on it. Then you'd have a great running, reliable, unique car.