I'm pulling the exhaust manifolds and motor mount...
wonder if I should install engine oil cooler lines (to radiator) and replace the trans cooler lines (for the additional external cooler)
I did this to mine when I needed a new radiator. I bought one that had the EOC in it and the OEM line set. Installed it during the next oil change. Removing the manifold and mount isn't necessary, but if you're already doing that then it'd certainly help.
Unless you're running yours harder than normal- towing, racing, lots of slow trail crawling, etc., the engine oil cooler isn't necessary. It's one of those not needed, but couldn't hurt things. I got my rad and the line set for the same price as just the non-EOC radiator, so it was a "free" upgrade. I've been known to run my Tahoe hard from time to time.
I'd like to get the trans cooler line set from the models that have the factory external cooler. I'd mod it to plumb in the Tru-Cool 40K I've been storing for about three years now.