NOS stock 340 cam from wholesaler worth the risk?

If I were going to install a flat tappet cam, I would make absolutely sure the lifter bores are clean and that the new lifters fit the bores freely and can turn freely. Follow the cam manufacturer's directions for lubricating the new cam with break-in lube. For hydraulic lifters you HAVE to check that the lifter preload is correct. You cannot assume that a stock replacement cam will have the correct preload with the stock pushrods, because it could be ground on a different base circle which would affect lifter preload. DO NOT soak the new lifters in oil, DO NOT pump the new lifters up outside of the engine installation. The lifters will fill just fine on initial startup. Another thing to watch for is lifter and pushrod spin. I have old valve covers which I temporarily install for initial startup, which I have modified with holes so I can visually verify that the pushrods are spinning. If the lifters don't spin the lifter/cam lobe will wear prematurely, and you'll send a bunch of metal thruout the engine, and you'll be tearing back into that engine.