Lovely lines these! I've read this Canto several times but one can easily gloss over such lines... The first line does not admit any other scansion. I experimented a bit with the second one: The All'|-Bliss'ful| sat' unknown'| within' |the heart';| But the amphimacer in my third foot sounds especially dreadful. It makes it a bit like |Stamp' your foot'|... In contrast, a small pause after "sat", which is understood in your scansion, makes the whole line beautifully balanced. The last line too is quite unusual too and reads lovely. Thanks for this sharing!