@weeksy the new crank will be fine on the HT2 converted BB as long as it’s not worn out. Just make sure there isn’t any play in it once fitted, otherwise replace it.
I’ve just removed my RF Respond single because it’s heavy and replaced it with an SLX triple and XT External BB that comes with it. I simply removed the three chain rings from the SLX and fitted the RF N/W I already had. Under £80.
Saved 200g and it doesn’t feel any less stiff. Love how simple the Shimano stuff is and the XT BB is only £13. On my other bike the XT BB lasted 1300 miles and still going strong. An RF one had play in it after 650 miles. No hosing / jet wash either.