A999 tranny same as 904?

rmchrgr is 100% correct with everything in his post.

Add your 5 disc high gear drum and low gear set and call it an 999.

rmchrgr is correct .. you'll find a factory low-gear set in a 998 or 999 lockup unit. (we offer the low gear sets at a reasonable price if you can't find an original lockup unit).

They are quick too .. NHRA compeition eliminator cars wouldn't use a version of the 904 if they weren't.

Don't forget to add your low band apply trans-brake valve body, and the mods that come with it. 8)