84 blazer 2.8 dead replacing with 4.3???

Can this be done reasonable? I have both vehicles already. Since I work for a towing company the 4.3 complete total was easy to come by. I want to put it where my 2.8 was... I have been told this cannot happen! ! ! I refuse to think I can ttrade em out. Can anyone help me with this or put me outta my misery and say its just NOT possible and back it up?!?!?!
Tips/tricks/links and websites are helpful and appreciated.

Jason

I have an 85 that I just converted to 4.3 TBI. I took the wiring harness dash computer and gas tank with electric fuel pump and put into my 85.
Works great was well worth the time to change everything. The 89 dash bolted right in...digital dash and all.
If anyone can tell me how to recalibrate the speedometer it would be a help though. The gear ratio's were different in the 89 and now my speedo is off about 7 miles per hour at 65.