open or closed drive line

[olfarmer]

On making my 40 pickup a better driver it was suggested changing out the four speed for a three speed transmission and changing the rear end gear ratio. In looking the parts I was wondering if it would be better to look for the 42 and up open drive line rear end and a three speed trans that would work. Is there any advantage to the open rear end verses the closed drive line. Any problems making the swap?
Thanks in advance
Mike