As far as 904's go if built right they can hold up extremely well to racing and strong street use and are minimum 2 tenths quicker than 727's. I have built a lot of these for friends in racing 2 of which run 9's and 10's and pull their wheels past the 60 foot mark. I have never had one come apart. If you use the proper stock internals and good clutches they will hold. 727's are great in heavy cars or trucks with big blocks but in a small car such as an A body or older B body with a small block the 904 is my choice.