The AR-3t's is not anything AR produced. It is an AR-3a cabinet and crossover slightly modified with AR-58 Teledyne era drivers installed. This particular set of 3a's had been abused. Only one of the tweeters was original. The woofers had been reconed and the mids had been replaced with some 8-ohmn drivers of unknown origin.
RoyC provided guidance on the crossover mod.
I wanted the cabs to match my AR-5 vintage look.
I still have the AR-58 cabs and crossovers although it is unlikely I will ever put them back into service. I don't have the time or space for those projects these days.
There are only a few of us who still enjoy these old dinosaurs anyway.
The AR-3a's that I see occasionally for sale on CL don't last long. They usually disappear quickly especially if they are offered at a low start price. The later models not so much. AR-5's are even rarer to see as production was only around 50,000 units I believe. They don't command a high price though.