Hi,
First post here so a quick intro.
I have a '56 Tbird and a '56 Mainline 272, 2bbl, 3spd.
Lots of good info here and on the "single barrel hollys" referenced already.
One more link that may help with your 1904
http://www.carburetor-blog.com/holley-1904-carburetor/
Lots of good stuff there and some videos. Also, just down a ways is a link to the 1904 Manual that was also referenced on the other thread from the Old Car Manual Project but this is a combined .pdf.
I would also agree Not to use direct manifold vacuum on the dizzy and just from the carb. The Load O Matics are very sensitive to LOW vacuum. It ranges from:
"1956 223 6 (1955 pretty much the same)
Distributor Vacuum Advance Data:
at 300 RPM: 0 - 1/2, Inches vacuum: .18
at 400 RPM: 1/4 - 1-1/4, Inches vacuum: .32
at 500 RPM: 1-3/4 - 2-3/4, Inches vacuum: .50
at 1200 RPM: 8 - 9-1/4, Inches vacuum: 2.59
at 1600 RPM: 10-3/4 - 11-3/4, Inches vacuum: 4.22
at 2000 RPM: 13 - 14-1/2, Inches vacuum: 6.00"
That is of course dizzy RPM so twice that for engine RPM.
The only way the springs for the vacuum advance can be accurately adjusted is on a Sun Distributor Machine that also has a Manometer accessory because the standard vacuum gauge on the Sun DT is not calibrated that precise at low vacuum.
HTH
Jim