Soloing with both hands on one's organ...

whilst not necessarily heavy metal, alan hawkshaw provides a good example. he was probably the best hammond organ player from the late sixties / early seventies, mostly as an uncredited session musician, but by the mid seventies he was noodling with moogs, and by the mid eighties was making dreadfully dull sequenced music.

there was always the feeling that heavy metal bands without keyboards were *more* metal - iron maiden versus europe, black sabbath versus uriah heep, etc. with this being the case, heavy metal keyboards probably fell victim to the wholesale rejection of the eighties pretty boy bands which has defined much of heavy metal since.

ultimate organ onanism = in a gadda da vida - iron butterfly, of course.

as per lineage, I'd say it goes further back than the late sixties/early seventies bands you mention to the organ-heavy garage bands, more like Animals>? & The Mysterians>Music Machine>etc.

iron maiden = kenny g of metal

The B3 on that album references the dirtified power chords of Jon Lord, sure, but there's also something new there. Bleak and cold, confusing, raunchy, funky. I don't know anything that sounds like it from the last twenty years.

Is it heavy? Sure. Is it metal? Academic. First, define "heavy metal". Modular conception of riffs repeated over time. Resolution into power chords, less of a concern with harmonic sophistication (one difference between HM and prog).

I don't think that the 80s redefinition of HM precluded the organ. I do think that when you play organ it's hard to keep your head out of your ass.

http://images.google.com/images?q=tbn:9TzV2DA9Jl4J:theband.hiof.no/band_pictures/GarthWails75_tag.jpg