PJ always has more insightful thoughts about stuff like this than I do, especially since it's his design. I'd imagine he'd specify a smaller cap if you planned to use the Speco output transformer, or something a bit heftier if you planned to use our current OT-2 or the Edcor-sourced upgrades for the older Paramours. Something around 7uF should be fine with the 60H/OT-2. I'd cut that value down a bit if you're planning to stick with the Speco.