i started at 4 inches and felt it was a bit too wide. It’s now about 3.5 inches which leaves enough room on either side of the transmission at where the motor mount is located. Once I actually start fitting the trans I will adjust the height of the upper crossmember to fit the trans. As you see I tried to follow the stiffening rib from side to side.
View attachment 1715497173
View attachment 1715497172