727 or 904?

If you are serious about racing and safety, here is what I've been using. If you cannot afford a dedicated race car and want to do street/strip with the same vehicle, then this might be overkill:
I've been racing a 727 behind about 750 hp for 4 years now.
1. Ultimate bolt in sprag from A&A. Sprag is Weakest part of tranny. Approx $200
2. Hardened steel or billet aluminum drum from A&A. 2nd weakest part. Known to grenade if you break u-joint and overrev motor. About $700 for steel
3. Reverse pattern manual shift valve body, with or without low band apply. This also allows you to safely raise pump pressure a little for firmer shifts $250 ($1,000 with transbrake)
4. Don't run transmission fluid. Use #303 hydraulic fluid. Again firmer shift, less slippage. It's cheap at Tractor Supply. $25 for 5 gallon bucket.
5. A good SFI rated flexplate. ATI is a good brand. use ARP converter bolts and ARP crank to flexplate bolts. $125 for flexplate
6. 5500 stall 8" converter. Performance Torque Converters is the one I use. $700-900.
7. Transmission blanket or shield. $125-400.
8. A good transmission cooler with it's own fan. $150-750.
I have a small block case with as many big block internals as possible. 4 gear planetary, big pump. Don't know if you can do that with a 904.
As I said it's been raced about twice a month 9 months out of the year for 4 years. Had it taken apart 2 years ago and it didn't even need new clutches!