Harland Sharp 1.65rr on PONTIAC heads - clearance?

I ordered a set of Harland Sharp 1.65rr and i've read on the net that i will need to clearance the pushrod holes a 'tad' to make them work..

My questions is how much is a tad? I know i need to grind material on the side closest to the stud but how far down should I go and how much closer to the stud should I go? Also, should I retain the guide plates with the Harland Sharps?

Regards

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BTW: the engine is a 1978 Pontiac 400cid.. the heads are Casting #16's out of a 1969 GTO RAIII (D port heads)

Thanks..