Someone has already modded your CJ by putting in the V8 but that is the original axle. It is capable of handling the 304 and larger engines to an extent but the AMC20 struggles with larger tyres.
The strength of the AMC20 is oft debated here as the axle shaft to hub connection is a splined one and can fail, as many of us have experienced, along with the tubes spinning sometimes under high torque. However with a single piece axle kit and welding of the tubes the AMC20 is used by many members with SBC V8s.
You may want to open up the diff cover and have a look at the internal condition and gear ratios before deciding. If the teeth are badly worn or chipped or the ratio will be wrong for your plans it may be a good time to find axles that will work with your plans rather than rebuild the ones you have. However there is nothing there to suggest you need to immediately replace them.
If you look long and hard you may find rebuilt axles with lockers and ratios suited to your plans for a reasonable price.
BagusJeep lives in Bali.
1981 CJ7 258ci - Bagusjeep
1984 CJ7 258ci - Puthijeep
1981 J20 258ci - Gladys
1951 Willys CJ3A/MB/M38 - Little Willy
1995 Cherokee 4.0 - CHEROKEE