I know the way they are ballanced and fueled changed but did the actual block ever have a MAJOR change?

I have a chance to buy a 89 engine for $100 and want to know if I could swap the block into my 99? I just want to use the longblock and put my intake and fuel injection if I can.

 

yes, I believe it did. I only know this because I just had my engine reworked and it was hard to find the right block. I can't recall the difference the shop explained to me. I had to get a new block because my old one could not have the crank journals bored because it would excede tolerances and allow the crank to "ride" to low and would wear out the rearmain seal..... here is a good write up on the history of the 4.3 The Chevrolet Small Block V6 Engine - Novak Conversions. hope this helps.

Give these guys a call they did the engine work and would be able to verify if it changed. http://www.mjmengines.net/

 

The 89 block will not have a balance shaft. It also will not have the same bolt pattern for the timing cover. Plus other changes...

You would be much better off getting a '96+ engine.

Here is an article that goes through the changes entitled Rebuilding the 262 by Doug Anderson up to '95, but doesn't have much information past that.

 

Thanks guys, I asked a 20yr+ GM mechanic too and he said the same thing...

I guess I gotta buy a 96+ longblock

 

Not that it matters, However I would like to add a few things.
'85- the first year of the 4.3 and it was only offered in fullsize pickups, had a two piece rear main seal and corresponding oilpan. Also had one less accessory mounting hole then a '93.

'96 + the angle of the heads to the intake manifold changed, along with the angle of the intake to head mounting bolt holes. Even if you did use a pre '96 block you wuold have to swap heads.

Also the '85 block had a mechanical fuel pump with a carburator. The block had the fuel pump mounted to the block, if you use it for a fuel injected motor you need to fabricate a plate to block the mechanical fuel pump opening.

Somewhere in the 96-98 years the transmission bellhousing changed. The bellhousing is now removeable from the transmission. This change also affeccted how the transmission botl up tot he engine. This also elimintaed the need for engine to tranny braces.

'94 and older used the old Data port, software, OBD1.
'95 uses a cross over between OBD1 and OBD 2, commonly referred to as OBD1.5
96+ uses OBD2.
None of that matters IF you swap all sensors, and fuel system to match your current engine.

Accessory brackets have changed over the years too, no big deal if you swap your current bracket over. You may have to drill and tap a new mounting hole. Or try the nused bracket and see if your wiring, hoses, etc will reach.

Finally, replace EVERY sensor in teh new block with sensors from your current block. The location of those sensors has moved over the years as well. Especially if nused block came from a Astro van or fullsize truck.

One last thing, make sure you reconnect EVERY ground wire. That includes the ones on the back of the block and under it up front.