In my restoration project of the 70 GTO I have my heater and A/C box out. Is there a way to ck the evaporator coil and heater coil for leaks and condition?

There are dyes that you can add into the systems to check for leaks. Most parts stores has them as a kit. This will require a black light to see the dye. Honestly for the cost of it I usually just use my mechanic for the job.

notallthere has an excellent point. Question, have you replaced the original evaporator and heater coil with new parts or are these the original parts that came with the car? If they are original, I would replace them with new parts and not risk putting a questionable part back into the system.

As stated, they are out of the car, new parts are expensive if the old sill work and can be refurbished.

OK, I re-read your question and perhaps I misunderstood the parts you asking about:

The heater "core" looks like a very small version of a radiator that is mounted up against the firewall instead the cabin. It draws hot water from the cooling system and pulls it into the passenger compartment where an air-to-heat exchanger pulls the warm air into the cabin. The inlet and return lines are connected to the engine. These can be tested and repaired by a competent radiator shop. Replacements units run $50-$80 plus shipping and handling from many of the OER catalogs. There is no coil that heats the water.

Similar, there is no "coil" in the AC system. The air conditioning evaporator core also looks much like a small radiator. It is typical mounted inside the large A/C housing on the firewall in the engine compartment. Unlike the heater core, this circulates freon refrigerate gas. So taking this to a competent AC repair shop would be my advice to have it tested. These cores are indeed expensive to replace at around $300 or more. I have always been told to replace the dryer once the system has evacuated and opened up to normal atmosphere. I would also have the AC compressor inspected and serviced at this time too.

Now would be a good time to investigate and consider switching the AC system from R-12 (freon) to R-134a since find R-12 is harder these days to find and expensive to purchase. It is my understanding that R-134a uses about 1/3 less refrigerant that R-12 too. Talk to an AC shop on the particulars about converting - what you should do or not do since I have yet to overhaul my AC system (its on the list).