First off about the Blow Fish: It was originally a P5-Hemi head- they grenaded that. Since they had to build another motor they wanted to go faster and now they have the R5P7 in it.

As you said; you saw they had put slugs in between the block wall and Floating Cylinders, they have band-aided the issue that many have seen and told you over the years why they wouldn't build a Boost application for that motor. HONDAs were notorious for this same configuration and Issue in their early years. Those guys Pinned and Plated there's and run some insane Boost and HP through those engines.

Making 1200+ with boost is not going to be like making 1200hp NA. NA you usually see a Trq Number that is 25-40% lower than the HP number. With Boost your TRQ number is going to up there closer to your HP number. something like 1200hp and 700ft/lbs=NA and 1200hp and 980ft/lbs=boosted. This is what is going to cause issues. TRQ breaks parts NOT HP. And Boosted motors have plenty of it. Same reason people short fill race blocks especially for nitrous and Boosted applications. Which those blocks have a solid fire deck.

Far as selecting parts: I call on the Pros. I to this day couldn't tell you the difference in a T4 or a T6 based Turbo. I called Precision and Turbonetics when I was ready to order mine and spent 2hrs on the phone with them discussing what I had what I was after and what I needed. After they both gave me the exact same setup details I knew what I needed and found a supplier. Now tell me what AR you have on the exhaust side and what MM the compressor side is and I know what you're working with.

Far as the fuel Pump; I'm going to be using MagnaFuel myself. I went with them for the simple fact they had an EFI-Package that fit my needs. Now they do have a Mechanical Pump available as well. Weldon is also a damn good choice. That's pretty much the only 2 I would even think to use. Always get more pump than you think you'll need. TOO many times I have seen pumps crap out from working too hard or plain out just can't keep up.

EFI: that's a whole another ball game in itself. I personally went with BS3 (Big Stuff 3) for the simple fact I could get all the things that were OPTIONS for FAST at the time were all included with BS3. And by the time I paid the Higher price for the BS3 it was still cheaper than the Fast if I added all the extras to Fast to make it equal to BS3. That was 2006. NOW?! Do your own homework and see what suits you best. I always hear guys say to get something that you know someone that can tune it for you. That used to be true. Not so much any more. Any of the good tuners worth a flip today can tuner either one. Same with getting help at the track. BS3 has become more dominant in recent years. But most that run BS3 have ran Fast in the past and know both systems. The same guy that owns BS3 developed the original Fast systems (Speedpro EFI) So they maintain a lot of similarities. There are other systems out there But they are usually more expensive or not up to the task.

Precision turbo has some basic info on wastegates and BlowOffValves on their website in a PDF file. IIRC it's under their FAQ link or something close to that.

Far as your Intake: Wilson Manifolds!!
They have about the best price I have seen for adding Injector bungs and Fuel rails to an Intake. They also have Throttle Bodies all the way up to 105mm for single blade and 2300cfm for a Dominator Style 4-bbl.

I don't know how well you know BondoBob (Bob Leeth) Bob's Pro Fab: But he was considering doing the same thing to his R5P7. He knows some Turbo experts local to him and they told him Boost would be no problem on that engine. The guys he knows deal more with Diesels and Tractor Pulls but they also run some diesels that have that same floating piston block configuration and Diesels Poor way more boost into them than a Gas engine would. 80-120psi

So all in all!!! Yes it can be built to do what you want and More. BUT your going to have to work with someone that knows what they are doing.

You might even look at bringing your RPMs out of the stratosphere to make the HP numbers your looking for.