Solid flat tappet every time. Of all the small blocks i have had over the years i have had the most luck with solids over hydraulics,i prefer a bit extra noise over a potentially noisy hydraulic lifter and dont mind setting lash every now and then.
With this type of horsepower they arent very often a daily driver so lash adjustment wont be that frequent and i like the ability to rev them reliably to 7000rpm with no issues,even though it may make peak power well before that.