For then guys have done it. If you were building a 904 for 650ish HP what would you do to it?

5 frictions in front drum
Upgraded tcs Spring return module
Good solid red lined band and hd band strut
4 pinion planets
Good vb and matching lever
Deep pan

That's what I remember from my build...with the right clearances I haven't had any issues making over 650hp...I actually snapped the output shaft with less power, but since replacing haven't had any problems.

Just my .02 cents

A good manual valve body
Later wide flex band 4.2 lever
5 friction front drum assembly with coil spring conversion kit
I like the blue plates
Rollerized rear support
A handful of the correct shims and washers to get the end plays right
Late model style converter hub and pump gears not a bad idea

Couple other little things. Everybody has their own little details they like to use. Or not.

Thanks guys. I have a CRT trans brake in my 727 that I can reuse.

Here are the notes from my 904 Build. 200+ passes and the last pass was the best yet. I took it apart for inspection and still looked fresh.

73 904 complete
4.2 billet front band lever (Cope Racing)
Cope Racing heavy duty band strut 
Cope Racing rear billet servo
New sprag inner race, springs and rollers
Cope Racing Front semi-rigid band red lining
Cope Racing Low reverse band red lining
Teflon pump support rings
Unrestricted pump support oil feed
Blocked front pump vent and relocated vent to upper tail shaft
Drilled front clutch retainer for quick piston release
Blocked accumulator - .002" clearance between piston and valve body
Front clutch:  5 - .061" Alto Red frictions, 5 - .068" Kolene steels.  Clearance = .060"
Rear clutch: 4 -.061" Alto Red frictions, 5 - .068" Kolene steels.  Clearance = .036"
Cope Racing 4 pin Low gear front planetary 2.74 first gear, 1.54 second gear (factory steel 4 planetary from Cope Racing).  Replaced thrust washer
Replaced all bushings
Used original rear planetary thrust washer
Replaced front clutch return spring with Cope Racing multi-spring clutch retainer
Total end play .013"
Gear train end play .009"
Front band adjustment - tighten to 70 inch pounds, back off 2 turns
Rear band adjustment - tighten to 70 inch pounds, back off 2 turns
Output shaft support bolts - 150 inch pounds
Pump body bolt torque - 160 inch lbs
Front servo pivot rod plug - 150 inch lbs
Tail housing bolts - 24 foot lbs
Pump to case bolts - 175 inch lbs
CSR transmission shield
ATI transmission pan - bolts 150 inch lbs
A&A Trans Brake - bolts 70 inch lbs (per A&A)
Air tested front, rear clutches, front and rear servos using 30psi air pressure

Thanks Humpty .

At 3350# with a 4.10 gear do I need a low gear set? I've been 1.40 60' with my 727 foot braking.

If you are running a stroker small block you probably don't need the low gear set. You just need the converter to be right. My car ran virtually the same when I took the low gear out of it. When I was running the stock stroke 340 it was a help.

Now having said that the newer style flat drive torque converter hub and pump should be mandatory. That slot drive hub is the weakest link in the the 904.

Glad to help. I don't have a comparison like Guitar Jones does, but I was about the same weight as you when I went from a standard ratio 727 to a low gear 904 and picked up 3mph in the 1/8th.

Be sure you use a steel 4 pin planetary. After seeing an aluminum unit I would never run one. Cope has them if you need one.

What years cores should I be looking for?

How much line pressure are you running

If you can find one 1975-1977 360 904 trans, which is a non-lock-up, wide 5 clutch front drum, little better sprag and steel planets.
I never have found one and used a early 80s lock-up and had a non -lockup converter made.

I've never checked it, my 727 has one of Cope's billet trans brake valve bodies in it.