You got some of it right. All 5.0's after 1981 have a 50oz imbalance so the flexplates on these two would be the same.. if they had the same transmissions. That's not a certainty though so you need to use the one from your truck.

The only wiring changes necessary are the sparkplugs which need to go to the HO order, the batch fired SD EFI in these trucks works fine with both firing orders.

The HO and truck 5.0 longblocks are identical except for the cam and pistons so this is largely a waste of time unless your motor is done. If your motor has life left then simply put a HO cam in it and you'll have the HO power output.. which is more top end HP with less bottom end TQ. And all upgrades from here on do more of the same so if you haven't done so already start saving up for some gearing.