I have a 89 RS with the 2.8 and 5 speed transmission.

My question is, can I swap the 2.8 with a 3.4 staight across.[]

 

3.4 out of a rear drive (Camaro) yes. Not realy sure though so you have to make sure you can install yourdistributer since the later Camaro will have DIS. There might be something involde with the cam and oil pump drive. But 3.4 were made for use with a distributer because that was a replacemnet engine for S10's.

 

http://www.engine-parts.com/GMV6/gmv6ps1.html
You might want to check out the above