Here's a breakdown of the challenges:
* Engine Bay Space: The 283 is physically larger than the stock 4.3L V6. You'll likely need to modify or fabricate motor mounts, potentially trimming the firewall or inner fenders to clear the engine and accessories.
* Transmission: The transmission from your 4.3L will *not* bolt directly to a 283. The 283 uses a different bellhousing pattern. You'll need to source a transmission (and possibly the associated adapter plate) compatible with the 283's bellhousing. This could be a TH350, SM465, or others, depending on your desired setup.
* Exhaust: The exhaust system will need to be custom-fabricated.
* Wiring: The wiring harness for the 283 will be different from the 4.3L's. You'll need to either modify the existing harness or source a harness specific to the 283 and adapt it to your Blazer.
* Cooling: The 283 may require a different radiator and cooling system components for adequate cooling, especially in a smaller engine bay.
In short, while not impossible, this swap requires significant mechanical skill, fabrication abilities, and potentially a considerable budget for parts and adapters. It's far from a simple plug-and-play situation. You'll be much better off starting this project with access to an experienced mechanic and ample mechanical knowledge.
