For installation with IMG archive editors other than Spark, follow another installation guide for similar mods.
For installation with Spark IMG Editor:
*Open GTA3.IMG in "Models" folder.
*Scroll to the very bottom.
*Remove () and version name within the () from a jetpack.txd of your choice and drag it right into spark.
*You will now see it in bold at the bottom of spark, the original has been overwritted.
(I've included a backup just in case you want to switch back)
*Do the same exact thing for the JetPack.DFF included if you want a better jetpack to go with that new texture.
Visit www.dertyjerzian.tk for some fun type stuff.