Looks like a great project.
Lots of folks have had good experience with the RH radiator, but that setup is just not for me. I absolutely must have a stock looking, fully function trunk. I'm building a daily driver / weekend autocross / long road trip car, need a trunk.
In your case, if you're going for an LS, you can still keep the trunk. Take a look at Reece's build here. He's using a stock Jeep Cherokee radiator tucked behind a 993 cover, and all he did was cut a RSR style duct. I've chatted which him quite a bit, he's daily driving it now, and cools perfectly.
http://forums.pelicanparts.com/porsche-engine-conversion-tech-forum/930992-new-project-76-993-gt2-widebody-ls1-subaru-box-996-brakes-3.html#post9836207
Only issue for me, is that setup won't clear an impact bar. Since I'm building a daily, I need to keep impact protection.
I'm a research engineer (engineering physics) for my day job, and I've done a lot of calculations on cooling requirements. I've also put together a big list of radiator options and so forth.
I've calculated that with my setup, I'll need about 200 square inches of radiator area up front. Assuming there's good ducting. Ducting is absolutely critical. I've done some air-flow models and determined where's the areas of the most pressure drop.
What I'm doing with mine, is I'm fitting a pair of Austin Mini radiators just under the headlights, very similar to how the 964 mounts it's radiators. For good measure, I'm also fitting a center intercooler radiator, so that should yield about 300 square inches. Should be way more than enough.
As for radiators in series vs. parallel. That's a complicated question, lots of physics there. On one hand, water pump volume is inversely proportional to pressure head. Pressure head is proportional to length of radiators. So, parallel yields much more flow. However, higher water velocity means way higher Reynolds number, which means greater thermal flow of heat from water to surrounding radiator. See, it's really complicated. I don't have enough hard data to create a good mathematical model, so at this point, going to have to try both ways and see which one is better.
Water pipe wise, in my case, I worked out that a 1.1" ID is fine, on an LS, with greater volume, you'd want to probably go with 1.25 ID.
I put tougher a photoshop of the style I'm going for. Yes, I'm totally ripping off Magnus Walker, but going for a more period correct look. I'd really like to do a full backdate, but sadly I don't have $10,000 for the steel parts. I'm going to make some cast aluminum grills, same style as the Karman Ghia to fit in the 964 fog lights, and these will be radiator air inlets. Will also duct lower inlet to radiators. Think I'll probably go with carbs also, I like the look.
I also put together a spreadsheet of different engine options. I thought long and hard about a performance VW T4 build, both N/A and turbo. That would have cost about double that of a Subaru. And in the end, if anything blows on the engine like a case, or other internals, I'd be at the mercy of ebay parts vultures, just waiting for someone gullible or desperate to pay their extortion prices. A N/A 2.7 swap and build would have been well over $20,000. Makes no sense for a 76 912 that's not even worth $25,000 in perfect shape. Weird thing is that flat-6 swapped 912 seem to be worth less than stock 912. So, why spend double what the car's worth on an engine to make the car worth less.
I've got a build blog / page here:
https://facebook.com/ArrowBlau
I've put together some spreadsheets and info on radiator sizes, shoot me a PM, and I can share them.
