Hi!
Take the FCOM 1, chapter "Performance Dispatch" B737-300 (I used the 22K engine rating tables).
Than
"Takeoff Field and Climb Limit weights - Dry Runway"
Using 15°C standard temperature at sea level, I found a Max field limit weight of 73400 Kg interpolating between the temperatures (the maximum value for the runway length is 11000).
Than, take the maximum Climb Limit weight: 63600 Kg (interpolating) with 15°C.
Ok, now you have 3 weights: Field limit 73400 Kg, Obstacle limit 62800 KG, Climb Limit 63600 Kg.
Go to the Chapter "Performance inflight" B737-300 K22 rating, you'll find a simplified method to correct the weight limitation for the antiskid inop situation in the "Text" part at the end of the chapter. That is 7800 Kg. Reduce the lowest of Field limit/obstacle limit weight by 7800 KG.
In our calculation the lowest is the obstacle (62800 KG) that gives:
62800-7800= 55000 KG.
Then, just below the Antiskid inop text information you have the V1 adjustment table. With 12000 ft runway length reduce the normal V1 by 15 Knots.....and pay attention to the Minimum V1(mcg)...