727 or 904

Guitar Jones said
The SS/AA Hemi cars (now SS/AH) were running 727 cases with 904 internals in them built by a company called ProTrans. They were good up to 850 HP. When the SS Hemi cars started exceeding this they went back to 727 internals.

The 904 is plenty strong enough for most racing and street car activities.

The 998 was used behind the 318 (4 front clutch discs)
The 999 was used behind the 360 (5 front clutch discs)
The 904 was used behind the bent 6 (most had 3 front clutches)

Dave Smith, the owner of Protrans has been building my 904s for years now and they still use 904ish internals in those 727s. I say ish since the parts are all custom billet stuff that he makes himself.

JW makes a bell housing that lets you put it behind a big block. I did it to my stock 68 Roadrunner that ran 13.77 at 101mph with a 727. After the swap to a 904 it went 13.39 at 106 mph. I am a true believer with my 10 second Swinger going 3 years and its still swingin'.