swartlkk I have yet to see much difference between the 4.3 1998 X and W engines. The X does not have the temp sensor on the front of the intake manifold like the W but the 'new' W was out of 1998 4WD automatic Blazer where the X was out of a 1998 S10 2WD.
Good news is that the 'new' used 4.3 engine was very clean when we pulled off the valve covers and the oil pan. As a reminder it was out of a 1998 4WD Blazer automatic with ONLY 119K miles.
However on removing the intake manifold it revealed the intake manifold gasket had not been replaced yet and was nearing the point it was going to start to leak.
We got the old 524K mile engine out of it today and when we pulled the manifold on it the gaskets looked new yet they had about 200K miles on them since they were replaced.
OEM intake gaskets are weak and replacement gaskets are strong is my take from today.
It turned out the oil pans were the same on the 2WD S10 and 4WD Blazer in 1998 in our case so we did not have to touch the oil pump/pick-up. Also throwing a rod through the oil plan did not cause any grief since we did not need the pan from the blown engine.
While doing the job I decided to upgrade to multi-port injector system.
We ordered ours yesterday from Amazon for $182 and it arrived today. Also order Scan Gauge II yesterday and it came today ($122).
I will not know if the MFI injection system will be a improvement or not since I have never ran this engine before but for $182 I feel better having the 14 year old SCPI injector spider converted to a 2012 MFI system.