Then this is a purpose built engine for a true purpose. I just cringe when I hear about people that go quoting HP numbers with stock equipment and then are disappointed when it doesn't drive well or has some other undesirable issues they didn't expect. It's just unfortunate that advertising with big HP numbers works to get parts sold. It just doesn't always work as well at marketing the best use of their product with the average buyer's expectations and intentions. But once the sale is done, mission accomplished, right?
The other thing I notice in your pic above is the oil bolt in the oil filter hole. Either that's a bolt from an oil filter relocation adapter or that's a stock Explorer bottom end you are working with. If it is an Explorer bottom end, those cast pistons aren't that great for performance. I wish I'd gotten more pics of my Explorer engine before I tore it down. But at the time, I wasn't focused on documenting what the engine looked like in stock form. I was focued on making it a 331 stroker!
Regardless if it is an Explorer engine or not, check the piston-to-deck clearance of each piston before you put the heads on. The stock Explorer engine I rebuilt had the pistons, on average .015" in the hole. If you've done that measurement before, I won't insult your intelligence describing how to do that, but if you've never done this before, ask how. It's not quite as simple as just using a gauge to measure between the piston and deck.
Point is if your compression calculations
assumed the pistons are flush with the deck, a .015" difference is enough to create an significantly lower compression than intended AND kill quench. Tight quench reduces the chance of detonation, in fact quench pads on heads are sometimes refereed to as mechanical octane. If after doing the check, you find that your engine has pistons deep in the hole like my engine was, there's a cheaper way to get that back without doing machine work. Use "thin" head gaskets instead of stock head gaskets. The stock Explorer gaskets from AutoZone are .047" crush thickness. Combine that with another .010-.015" distance with the pistons in the hole, and you have no quench to speak of. A set of .025-.028" thick gaskets would be worth considering. Although they are pricey to the tune of $80-100 each!!! However if this is for racing, that's a fairly low price for improved detonation control AND a bump in performance.
Despite what Ford says their stock engine specs are, I found their adherence to not be as tight as I once believed them to be. When I cc'ed my GT40p heads, they were supposed to be in the 58cc range. I found them closer to 63cc. Even after having .010" taken off at the machine shop, every compression chamber was still over 60cc.
If you want more proof of lax engineering tolerances on those heads, check this out...
Head1, chamber 1:
Head1, chamber 4:
Head2, chamber 4 (what would be cylinder 5 if mounted on the DS):
Ford considers this perfectly acceptable on a truck oriented production engine. And if all you care about is emissions & getting the engine through the warranty period, these differences are of no concern. But if you are looking for consistency in cylinder-to-cylinder performance and are looking to optimize as much performance for the purposes of racing, you might find this a bit more concerning than Ford did. And I see you are going with aftermarket heads. That's good, you don't get that kind of "slop" on most aftermarket heads. But if you are using a stock bottom end, you might want to check things like the deck height.