[AJD] Carb for 1951 A

[Eileen Brazil]

A friend of mine has a 1951 JD A, almost the last one built, and needs a carb. (What he's using is a B carb - not working well at all!)
A JD book he has says the carb should be a DLTX 51, Robert's carb says it's a DLTX 71. What is the right carb for this tractor, please??  Where might he find the right carb?  Thank you.

Thanks - the W stationary engine I asked about previously is a 1946.

Eileen Brazil
1949 D, 1956 420 U, 1955 40 C