What size valves are in the HO heads & how do they flow compared to the GT-40 & then the edelbrock & then AFR's.
The HO E7 heads use 1.78/1.46 valves, the GT40 1.84/1.54, and the GT40P 1.84/1.46. Typically, in stock form, there is a 15ish HP gain from E7 to GT40, and another 5-7 to GT40P - about the flow of the old C9OE and D0OE 351W heads. That's with stock lift cams. With higher lifts, the non-P heads actually do better. These gains are only realized if tuned to obtain them. You'll actually find the factory lower intakes are the bottleneck and why the Cobra and Explorer intakes are so popular as a first-step upgrade.
Where the issue lies is that they can be ported by experts for much better flow (the flow patterns are bit tricky in the GTs especially), but the expense pushes costs to where the HP per dollar begins to favor the aftermarket heads and their additional room for growth.
For a street/strip 302 to 347, the AFR165 and 185 shine, and especially the TFS Twisted Wedge 170 series as one of the best values in HP per dollar. The Edelbrocks are great for a 302, but will need a little massaging for a typical moderate to hot street 347. You'll find that flow numbers are all over the board on these heads (and other possible candidates), and actual user results are the best way to weed-out the better choices. Note these are for 'as-cast' heads, and so there is more room to grow with porting later as required.
This question does not concern heads, but with a 347 stroker i have heard of excessive oil consumption due to the wrist pin in relation to the oil ring??
That was true many years ago, but the legend continues. These days it is rare to find a 347 piston that has the pin and rings intersect, and it has been a long time since they have been regarded as 'oil burners'. Just pick a combo that does not have intersecting oil rings and pin holes and you're good. Also, if it's a street car, do not use low-tension racing rings - another source of the legend for other engines as well.