650-675whp on 94 octane pump gas, and worrying about bending rods/etc really aren't going to happen simultaneously. The rod-killer/main-killer is a combo like a 6266 or 6466 that's all-in on E85 and making 800+whp and similar tq figures. Generally speaking, so long as you don't exceed ~650wtq below 4500rpm you're going to be fine.
You won't likely see that happen on pump gas no matter how good the pump gas is.
Also, a glaring omission from your parts list is a standalone ECU. If that's because you've already got a tuner and a quality EMS in mind and you're just sorting out the hard parts, disregard. But if you haven't considered that yet, that is absolutely the most crucial component in this setup.
But if this were my car to build:
Camshaft= GSC S1
Valve springs= GSC beehive
Retainers = GSC Ti
Valve seals, leaning towards OEM= OEM is fine
Head studs(if necessary)= the shelf-stock ARP 2000 head studs are fine, and cheap insurance if you're in there. For sub ~900-1000whp setups there's no need to go to the exotic options such as L19, CA625, or 1/2in custom studs.
Headgasket(if necessary)= Toyota OEM 2JZ-GTE headgaskets have held 1400+. No need to reinvent the wheel here.
Turbo= DBB every time in a road race car. The transient response difference is well worth it on a road course or when canyon carving. I given your pump gas goals I would strongly recommend a newer Garrett GTX Gen 2 option, specifically a GTX3582R or perhaps the GTX3584RS - Unfortunately when going for 600+ on pump you will need headwork and you will need a larger turbo because you just have to move more air mass per psi of boost. If race gas, E85, or methanol were options you might be able to go as small as a GTX3076R Gen II
A DBB Gen 2 PTE 6266 or 6466 would also be strong choices. For road racing, I would avoid any of the Borg Warner options in that size range because they're significantly lazier in transient response. They are durable, though.
Regardless of the turbo chosen, I honestly gravitate towards the larger turbine housings, especially when going for max HP on limited boost/limited octane, and doubly so in a road race/lots of long extended sessions of full throttle/full boost. Larger turbine housings mean reduced backpressure and lower EGT's. With modern turbochargers the response doesn't suffer in larger housings as bad as it did with the old school stuff.
Exhaust Manifold= The FSR/SPA turbo cast T4 manifold, no question. Hard laps will eventually crack virtually any tubular manifold and the FSR/SPA manifolds have gone over 1200whp so I doubt there's much in the way of meaningful restriction at your HP level, and the durability and spool advantages will be very much worthwhile.
Injectors= Any of the quality EV14-based 1000-1300cc options would do just fine. Injector Dynamics and Fuel Injector Clinic both have great options in those size ranges. Again, the best injectors in the world don't mean shit if you're running a garbage ECU or you have a tuner that doesn't know WTF he's doing.
Other Parts=
-4in Downpipe/Midpipe regardless of catback size or choice. It does wonderful things for response and HP regardless of the boost level, turbo size, or anything else. It's faster spool and more HP and less backpressure everywhere. Win-win-win-win.
-The 044 pump was a hero in its day, but now it's the HKS T04R/GReddy T78 of fuel pumps now but without the sweet nostalgic sound or look under the hood. Newer Walbro 416/450 options would achieve your HP goals on gasoline (and even E85 depending) with a single pump, but the 044 will not.
I would strongly recommend the Radium Auto fuel pump hanger for the MKIV, and pretty much everything Radium makes that I've seen or installed on customer cars over the years has been of outstanding quality. If I was starting myself from a clean slate, I'd just throw the Radium Auto catalog at my MKIV (rail, regulator, FPD, catch cans, pump hanger, etc) and call it a day. If you already have another rail/lines/regulator kit, no need to change them to Radium parts just because.
With your HP level, too, you don't need to get crazy with fuel lines. A single -8AN feed from your Wally 450 to the firewall side of the rail and using the stock feed line as a return line will work just fine, and save you a lot of headache on fuel lines and fittings. That combo will go as far as one Walbro 450 can without any fuss, too.
As an aside, I moved this out of the technical subsection as this is more of a 'performance/modification discussion' sort of topic. If you wanted to get into the engineering-level details about specific components or really get into the weeds on a much narrower or specific issue, the technical subsection is the best pick.