Buy a complete engine. Taking care of the timing chains requires hundreds of dollars of specialized tools......and taking care of them is required because you're taking the heads off. Just buy a low-mile used complete long block. A buddy of mine is currently replacing his blown head gasket 130k '02 4.0 for a used '02 4.0 w/ 40k for under $400.
You can use any 01+ SOHC. I suggest the newer, the better for the updated timing chain guide and tensioner design. Some say the issues were fixed in '03...others say 04. I chose a 1,000mile used '06 4.0 for my engine swap. The $1000 price tag was ALOT better than just doing timing chains on a 110k beat up, sucked in water 4 times engine at the cost of $1500-1800. Made ALOT more sense just to buy a used low mile complete engine. The swap from 01 engine to 06 engine and using the '06's sensors required me to use my stock 01 harness and cut and crimp the different pigtails. The differences were fuel injectors and DPFE sensor. That was it.
Check out Car-Part.com--Used Auto Parts Market
. It's a parts search engine of tons of junkyards and their inventories. It's how I found my 1,000 mile '06 4.0 for $1000.