oil pressure and adjustable hydraulic valve adjustment

Saturday I out the valve covers back on and started the engine. It still has the problem on #6 exhaust which cause a miss, especially noticeable at idle. But overall the engine is running smoother. My guess is the valves were too tight after the oil pressure was boosted with the replacing the distributor oil plug. Could this be the case?

My machinist says to bring the engine to him and he will fix it for between $800 and $1450.
Does that sound reasonable?

thanks!