if your question is will they bolt to the head[bolt&port spacing] buy header gaskets for the heads and match them to the header flange ,they can be returned.
The bolt pattern and exhaust port spacing did not change so those headers will bolt to gt40p heads, you may still have trouble with some of the plugs/ wires because the plug angle is different on the p heads,
Those headers will be problematic with P heads, hell you're gonna have problems with the plug angle with any header on that ranchero, maybe the shorty style headers from mac for a fox body will work but no guarantee. I would use a different set of heads.