The graft will definitely succeed, and will succeed even if the variety is not quince-compatible. That is a way to graft a non-compatible variety onto quince. I have done it many times, its easy.

The precociousness is from the rootstock primarily so it should be the same. If the interstem is genetically vastly different than the top variety it can have some effect but the interstem is similar to your top so it should not have much effect.

Scott

Thanks a lot for the info. BTW Tomcot and Moniqui are full of flower buds thanks for those recs.