Ok, so it is not an exact comparison (SBC 350 vs LS), but similar enough (size, weight and aero dynamics) to get me to chime in on the subject. When I built the cool pack on Lance's Suburban I put an 11x11x1.5" thick Long plate trans cooler in front of the condenser (as well as a power steering heat exchanger). As per his request, it does not run through the radiator at all. I did install a fluid thermostat before the core because I did not want it running too cold when we travel in winter months. I also installed a trans temp gauge (if you don't have one, you NEED one--extremely important where you/we run). With this setup, he has yet to get the trans hot except on a trail running in high range and lugging the motor instead of low range and spinning the motor in its power band. Threw it in low range and trans temp dropped to normal range instantly. Other than that, no issues whatsoever.
The radiator he bought was a real POS. It was a new copper/brass, but a low efficiency core. You could drive a Mack truck between the fins and not even have to pull the mirrors in. I put two 12" Spal fans on a shroud that covered the entire core area. Even with the completely crappy core, it rarely ever got up to 220*. I have since removed that radiator setup and installed a monster aluminum radiator with two rows of 1.25" tubes, It has two un-named 18" fans on it and so far it seems to do very well, but as you well know, it's still cold out. 90* during the day will not test a cooling system here, but it sits on the stat all day long. If I was going to re-radiator a truck like yours I'd look at an industry number 730 radiator. It is the big four row radiator that came in trucks from 73+. The current replacements are two 1" row aluminum core and plastic tanks. This is the same radiator I run in my truck, but it's a drop in for your truck. The bushings are available in OER under part number 6264100. Huge aluminum radiator for about the least money you can spend and, if you buy it from your local radiator shop, you'll probably get a lifetime warranty on it too. This also gives you a huge surface area to put some big ass fans on. Having run a few different brands over the years, I only run Spal anymore. They cost a bit more, but they seem to last longer than any others I have used.
As far as the stack-up in your cool pack; without seeing it, I would offer my opinion to leave the trans cooler in the forced airflow in front of the condenser in front of the primary electric fan. I would also leave the power steering cooler up there as it doesn't take too much to keep the ps fluid cool. If I was relocating any heat exchanger it would be the engine oil unit. The reason I am wanting to relocate that is because on anything other than higher speed highway, an engine oil cooler really doesn't do much. I am basing this on research done on a vehicle with an oil temp gauge and vigilant monitoring of it. You could even mount it right under the core support with a fan or even a simple air scoop on it and be fine. I like as much simple as possible.
Also, keep in mind, when you actually drive your vehicle on roads at speed, your cool pack absorbs bug guts like a sponge and needs to be cleaned out any time you have the opportunity. I had my radiator out last week and was showing my boy how to clean the fins and we were both amazed at how much crap we got out of the core area. Absolutely amazing. I even soaked the condenser and CAC with simple green and washed it out from the engine side forward. Got a bunch of junk out of those as well. I installed a stainless screen behind the grille for bug abatement, but most of these were smaller than the openings in the wire cloth I used. Not saying your problem is related to this, just a reminder to make as big of a mess cleaning stuff out as possible when you have it apart.
Good luck. You have my number, feel free to use it.
