You should be fine with 1.500 .250 wall (1.00 in ID x 1.500 in OD) DOM.
Ballistic fabrication sells weld in 3/4" tube adapters.
http://www.ballisticfabrication.com/...er_p_1431.html
I would run the same for the upper link. 1.250" .120 wall has served us well in the past.