only too long but sits too low and fan hits crank. Additionally, the 55 water pump turns slower and is designed for a pressurized system. I've had much better luck making the following adapter:
Gather a 55 water pump gasket, quarter inch plate and a 41-54 water pump. Remove plate and gasket from 41 - 54 water pump. Place gaskets on quarter inch steel plate plate so 54 pump mounts in stock location and upper water passage align. Cut as shown in picture. Lower water passage will look like quarter moon.
Tack weld flat head machine screws to plate. Screw plate to block with 4 bolts. Slide water pump on 4 flat head machine screws and attach to top 2 flat head screws with head removed. This means you have to pull the head to change the water pump. Using quarter inch steel plate, I've attached the plate to the block with only 3 bolts and have had no problems. It leaks with a thinner plate and tightened belt.
I have not used a 37 - 40 water pump but imagine it would work as well.