A few folks here have installed EB tops on RBs and RB tops on EBs.....
Installing the top on the van it was designed for is challenging enough as you may imagine, esp getting the dimensions and location of the roof hole correct, since you get one shot at this.
Here is one thread about doing a transplant
https://www.sportsmobileforum.com/fo...top-10808.html
Used SMB tops are usually $2K-$3.5K-ish depending on condition and whether or not it's a manual top or a power top.