Unless you can see a "type B" gas vent assembly marking on the transite, it is considered the same as single wall metal per today's codes. Transite hasn't been used for gas vent chimneys for many years and the level of inspections for mechanical even 15 years ago wasn't too good in Contra Costa County (I have a lot of experience in the area over the last 32 years). You will find many old asbestos cement gas vent chimneys tight to combustibles, not too bad a condition if there is a good draft hood like a water heater but can be a heat hazard to wood for an appliance like a mini boiler. Check the ceiling construction, if the ceiling is regular plaster, no problem; if gyp bd, cut at least 2" annular area around the transite pipe; if any wood is part of the ceiling, cut at least 6" annular area around the pipe and make sure no wood is within 6".
A vent connector does not have to be listed product between the draft hood and the type B gas vent chimney, only has to be of the proper metal guage, thus adapter can be custom fabbed and mechanically fastened (very carefully drill the transite & use simpson concrete "blue" screws.