The 7.4 ltr has the same block as the later 8.1.
If I was doing the swap I would go with the GM 8.1 crate engine.
Our 95 Burb had the 7.4. W3:73 RE. (with numerous mods for mpg)
When we got our 06 8.1 W4:10's I was concerned about poor mpg, BUT as it turned out even with the added displacement and taller gears it is averaging almost 4mpg better.
Just my take....
Good Luck with the project, keep us posted.
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