tranny swap or engine swap

I've got a 89 s-10 Blazer 4x4 with the 4.3 and the tranny's not shifting.
I can get my hands on a 89 fullsize pickup 2wd with a good tranny but it's a 305. My question is is it easier to swap motors or trannies? and if it's even an option before I purchase the pickup?

Motors should be the same but 4W and 2W transmission are different.