Mob heads with candles have a pretty occult vibe going on, so it would be nice if they gave enchantment power like stacked books do!

I'm pretty sure that they do

Tho on forge only

They don't appear to. I thought it might be a 1.20 issue so I did clean install of 1.21 with latest neoforge and just Amendments, JEI and Jade mods installed.

There's no "ench power" tooltip on the heads, no enchanting particle effect like with bookshelves and they haven't moved the needle on the enchanting level.

I know In 1.20 they used to at least, they even had company with quark candle ehcnanting. Maybe having quark was a requirement I forgot

Placeable books and crystals on pedestals work?

Yeah, both are working fine on my 1.20 pack.