Try tapping on the starter solenoid, mine was doing similar things and this simple problem fixed it. Give it a few whacks on the end with a small blunt object. :explosion
If that does fix it, the starter is on its last leg, could last many more months, never know, have it tested.
Also try cleaning the connections to the starter, and grounds to engine, the combination of those few things made it start better then in recent years.
Those were my first thoughts - until I saw that "sat for six years" bit.
Concur - MMO down the plug holes, let sit a bit, and then test crank. If you can't get Mavel Mystery Oil locally, mix auto trans fluid 3:1 with acetone and use about a tablespoonful of that down each hole.
If it cranks over better (charge the battery, pull the starter and have it tested while you're about it. Charge the battery with as low a charge rate as possible - under 5A is good, 1A is best
then change the oil, put the plugs back in, and see if it kicks over.
If it doesn't, you've eliminated at least one problem. Once the starter and battery are "known good" and the engine cranks over quickly, look at your CKP (CranKshaft Positon sensor) next. It's a common cause of "crank, no start" issues on XJs in general.
Another good thing to check is the silly little ground strap from the cylinder head to the firewall - probably just replace it outright, since it's twenty years old. Better to use actual wire - use 10AWG as a minimum size, with a 1/2" ring on the engine end and a 3/8" ring on the firewall end.
Alternatively, just run the other end of the chassis ground (that's what it is - the primary chassis ground. A/K/A "The RENIX Killer") to a screw that's easier to reach - one of the fuel rail mounting screws will work neatly. You can then use a 3/8" ring instead.
That ground strap is the primary ground channel for the chassis. All of the sensors ground to the engine block, the ECU (Electronic Control Unit) grounds to the chassis. If that strap is failing or contaminated, it will raise all sorts of Hell with your sensor signals - and cause crank, no start issues of all varieties! This can be tended to while you're soaking the rings in MMO or ATF/acetone and charging the battery.