First, I agree with the guys above and run solid flat tappet 99% of the time and have never had an adjustment change with aftermarket rockers, even after years and years. Stock rockers if loose adjusters, different story, but that is a rocker issue not a cam issue and will apply with a hydraulic cam as much as a solid. In your case, I'd either see if you can change the adjusters to the lock nut style or go with aftermarket roller rockers or crane iron adjustable
However, depending on the RPM you normally run, the cam choice isn't bad. A 280H or XE274H cam is a nice street cam for a 428. However, I think you are being overly conservative with compression and those pistons are likely not a good choice because of that. Essentially you are compounding conservative things which gives up power.
First, the compression height, rod and 1/2 stroke stack = 10.150 with that piston. That's .020 below, add in a .039 gasket and it is getting loose in quench, low in compression. Assuming a 76cc chamber (iron tends to run on the high side) that's 8.88:1 compression, 9.12:1 if you zero deck. Even zero decking, the 280H cam on 106 comes in at 7.24:1 DCR, which is giving up some torque and power. Most shoot for just under 8:1 for conservative builds and about 8.3-8.5 for guys who don't mind watching for the right fuel, you are well below the conservative side and giving up power.
I think at the power level you seem to be searching for, I'd consider a 14271 Probe piston, it's a little shorter, but a 16.9 reverse dome. Cut the block to 10.155, and run a .030 Cometic if you like those gaskets. In addition, when you work the heads, cut them a little for a good sealing surface for the Cometic as well as ensuring you get to 74cc or less. That combo at 74 cc gives you a 9.8:1 compression and tight quench
Then a 282S solid flat tappet cam is really a better choice than the 280H for power, and with a little fudge factor for lash, gets you to about 8:1 DCR on 106 ICL.
If you really want the hydraulic cam, it drops it to 7.7-ish DCR and will run well.
Other than that, I agree on the oil pump that it's not needed, but I don't think it'd hurt either if you already bought it. I run an HV/HP in my 445 and an HV in my 489, and neither are restricted, but historically on cold mornings the 445 sure does climb in pressure, but I just run a good 10w40 and life is good. In theory, compensating for the high pressure with a thin oil may assist in drain back but at that point I am just justifying my combo LOL
Thinking converters is good too, most guys miss it, but again, do not go too conservative. A 2000 stall is likely only 200 rpm different than stock, Fords have a bit higher stall than your common Chebby, I'd be considering a good brand name 2400 rpm stall if you are spending the money or maybe leaving alone. In the end, more stall will help and the fear of cooking the tranny really doesn't apply.
Your comments on the heads make me think you are underestimating the power there. A light clean up on the ports and bowls generally means going cheap/stock In my opinion, the valve job, to include the transition to the bowl and the guide area is cheap power and if you need valves and guides, consider at least an undercut stem, but going 11/32 would only help without too much more cost.
I would have someone who knows what they are doing do the heads. Even if you don't get fancy with valve selection, a modern multi angle valve job and bowl clean up will gain you great power per dollar. The ports, not so much, although I'd consider matching the top and sides to the RPM and ignoring the bottom as your heads will have a significantly lower floor, and having the MR port enter the head high can only help
Finally, I think the rod bolts are a good idea when prepping the rods, but I do not think you need main or head bolts if you are watching the dollar. Its a few hundred dollars that really won't do much for you, especially head bolts. Seems like blasphemy to say, but certainly Ford head bolts do well with iron heads. The mains could be done for insurance if you cannot sleep at night, but if the mains torque up well, I don't see it as a requirement. FWIW, my 489 has all aftermarket bolts except for the cross bolts head bolts for room and mains for the hell of it, but my 445 uses all Ford bolts and I have never had a main bolt failure ever on an FE, assuming the bolt torqued well at assembly. If it didn't I just replaced it then.
Good thought on the entire build though, just a bit too conservative when you add repeated conservative choices IMHO and I am pretty conservative
