Dumb question: did BT7s come with a balancer originally, or are you looking for an upgrade, or ?
You might try these guys. They rebuilt my BJ8 damper and I was pleased with their service.
https://www.damperdoctor.com/
I wanted my original BJ8 damper rebuilt, so I sent an inquiry to damperdoctor via their website. No response -- ever. I did it again, same result. I called them, left a message. Same result. Did it again, same result. I can't say I was impressed with the interest damperdoctor showed in providing customer service.
I ended up buying one of those expensive ProRace dampers from Moss after I saw one on someone else's car. Installing it was fun, since the X-brace in front of the radiator restricts the ability to swing a hammer, which you have to do after jacking the nose of the engine up to clear the cross-member and heating the thing up to drive it onto the shaft. It looks like a quality item (as most things made in Australia are), but the damper was built for Chevy's, etc. and happens to be listed as applicable to A-H 3000s. The numbers and degree markings on it are intended to be read from the left (driver's side, LHD cars), instead of the right like God and BMC intended. I didn't think the markings would stand out very well against the shiny silver damper, so I marked 15 deg. BTDC on it with white paint before installing it. I'm glad I did.
I called the ProRace technical support phone number in California to discuss an issue. The number got me Sales. They referred me to a specific guy in Chicago. I called him and discussed the difficulty of installing it with the hammer because of the X-brace. His comment was "You seem to know more about Healeys than I do. I'm gonna keep your number and refer anybody else who needs help to you!". I haven't heard from anyone yet :highly_amused:
One more thing: the center recess of the ProRace damper where the dog nut goes does not allow room for a washer to be bent over to lock the nut like the original. I used Loc-Tite on the threads before torquing the nut to 90 lb-ft. I hope it stays there.