Very, very sure. (-;
Just for fun, you might like to compare these others, which are also regular
(-ed) in AE but irregular (-t) in BE (at least in older texts; some of them may now be changing in BE too, I'm not sure):
burnt, dreamt, dwelt, smelt, spelt, spilt, spoilt
"Burnt" as an adjective still exists in AE, though it may be gradually disappearing: burnt toast, burnt sienna (a crayon color). The phrase "Don't cry over spilt milk," which may have survived longer as a fixed expression, may now be mostly "spilled" in AE.
"Leapt" and "leant" also sound a smidge less foreign to me. I might use the former but never the latter, which doesn't seem logical, sorry. But for many AE speakers I think both are now generally regular.
"Knelt" is still used fairly widely (at least by me) but apparently "kneeled" is making inroads.
But the more I stare at these past participles by themselves the weirder they all start to look. So I may well have gotten (now there's a beautiful participle that's archaic in BE but entirely correct in AE) some of this wrong. If so I trust someone will step in.