I bought the car with engine needing attention, so compression tested the cylinders, which were all vastly different , then removed the heads and valves and sent them to an engineering company to have the valve seats recut and the valves ground in.1970 Pontiac Trans-am 400 cu in owned in 1977. Lovely car, used loads of fuel and too expensive for a young lad to run!
The problem was the first two companies I approached wanted to know what the heads were off because they hadn't delt with such large valves before and didn't have a valve seat cutter big enough.
On a recommendation i took them to Walthams in Bognor Regis who were able to complete the job.
One exhaust valve was so pitted I had to source a new one.
I collected a new top end gasket set from EJ motors in Streatham then put it all back together.
Phew it ran like a watch, (lots of ticking) no seriously I was very pleased with the result, smooth and powerful and a pleasure to drive : Incidentaly the car was bought new in America by the Helena Rubinstein cosmetic company in New York who used it as a promotional vehicle.