Running PAC 1326 springs at 2.00" install height. I think the retainers are +0.100", and PAC machined down the spring locators to 0.030" thick.
Running a hair less duration, but 0.726" lift with the T&D 1.6:1 rocker arms. I think the retainer keepers were stock, and running lash caps.
Got a deal on the springs from my cylinder head guy (paid about what the 1200 series cost) who had them for another project where they were not used (or the guy bulked at the cost?)
My cylinder head guy setup the install height so not sure on the keepers used, but I recalled the special order spring locators, and retainers were all from PAC.

My old setup used PAC 1325 springs, and the +0.100" Ti retainers from Crower with Manley spring locators. I think that setup may have used +0.050" keepers.

Make sure to check piston to valve clearance with that much duration.