Welcome to the forum Jason,
Sounds like you have a plan of attack on your restoration. The earlier 61-68 trucks used the bell housing as an engine mount vs the tranny and it is also a cross member. Dodge pretty much just cut the cross member to install auto's and added a cross member to support the tranny.
I'm sure some of the other guy's will chime in on this and there is different ideas on how to do this. Some guy's do it just like the factory did and some reconfigure the cross member to add strength to the frame, so it is a preference thing as to do the conversion.
You will definitely have to find a tranny 2wd auto cross member and modify or remove the original engine bell housing cross member, other than that it will be pretty straight forward.

My opinion on it, is to just cut the cross member out and box the frame at the shackle mount so it will reinforce the shackle mount area of the frame.

Mark D.

1968 W200 Sweptline
1969 D100 Utiline
1971 D100 SE Sweptline
1993 D250 Club Cab Sweptline
1986 W250 Cab & Chassis
1978 D300 Sweptline

E. Brookfield, Massachusetts