Avenirs are great motors. They are newer than the BB and use pretty much the same parts as the US DE. But the upper oil and lower oil pans are different as they come from cars with AWD trans. With the Avenir manifolds you can upgrade to a GTI-R t28 unlike the BB's Sometimes they need a little grinding to clear the crossmember. There is also one less bolt on the drive shaft retainer part on the back of the block (same as all dets). The t25 will need re-clocked or you will need a custom dogbone mount. Thats all I can think of