The NMR record (available through Coflein) describes Meinillwydion as a stone pair:
Two erect monoliths, 30m appart. The northern stone is known as ‘the pulpit’. Further stones are noted in the vicinity.
The Landranger Ordnance Survey map implies that there are four stones, and from the road three are visible. The eight figure grid reference cited on Coflein is SN43181019.