If any of you gentlemen are looking for a Suzuki 4ls drum I have one. But I want $600 for it. On drums for racing smaller capacity bikes the 2ls from the CB 72/77 or CB 450 is a good drum. I use one on my P5 500 yamaha. They are also P4 correct. Curly
Here is some good info/comparisons.
I can't see the CB400 listed. 
http://www.eurospares.com/drumbrak.htmSuzuki drum brakes
Model         OD x shoe width    Swept area   Radius x S.A. 
                  (square inches)   braking coefficient
GT550/750 4LS (200mm)   7.81" x 1.0" wide (x 2)   49.07      191.6 
T500 (1967) (200mm)    8.00" x 1.6"        40.21        160.8 
T350 (1970) (180mm)    7.12" x 1.12"        25.06         89.21 
X-5 Invader (160mm)    6.25" x 1.09"        21.4         66.87 
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Kawasaki drum brakes
H1R 4LS (250mm)    9.87" x .75" (x2)      46.53       229.74 
H1 (1969) (200mm)    7.90" x 1.4"       34.74      137.22 
A7SS (180mm)       7.00" x 1.2"         26.38        92.33 
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Yamaha drum brakes 
XS-650 (1969) (200mm)    7.80" x 1.3"       31.85       124.2 
YDS-6 (1967) (180mm)    7.02" x 1.17"       25.8          90.3 
TD3  (260mm)      10.29" x 1.06" (x2)   68.53      352.6
   entire front wheel assy, inc. 19" alloy shoulderless rim (36 spoke), axle and 
   TT100 tyre and tube (and valve and cap!)is 18.5 kg.
   Each brake backing plate assy: 2.25kg
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Honda drum brakes
CB350 (1970)  (160mm)    6.30" x 1.4"        27.70         87.25 
CB175 (1971) (160mm)    6.20" x 1.18"       22.98        71.24 
CB77/1968 CB450 (200mm) 7.88" x 1.18"        29.21      115.08 
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Bridgestone
350 GTR (190mm)    7.40" x 1.2"        27.89       103.20 
175  (160mm)       6.20" x 1.18"       22.98         71.24 
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Bultaco drum brakes
250 Metralla (160mm)    6.30" x 1.6"        31.65        99.69 
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Ducati drum brakes
250 (180mm)       7.08" x 

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Bianchi
500 GP (230mm 4LS)   9.5" x 1.25" (2)   74.61       354.41
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BSA 
Gold Star (200mm SLS)   8.0" x 1.375"      34.60       138.42
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Moto Morini
350 Sport (Grimeca 230mm Dual-SLS)
         9.05" x 1.16" (2)   65.96       298.47      
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Munch 
Mammut 2LS      10.0" x 2.0"      62.83       314.1