hey macho, I'm near Portland.

Not too bad a swap.
Mounting- the later blocks should still have the mounting ears for old style mount brackets and thats a breeze.
Fuel- Your 1990 stock tank has a pump capable of feeding 38 psi and maybe more. A believe a 2001+ runs at 58-60 psi or so. If stock pump is a no go, a walbro replacement will fit when the rubber lines in the stock fuel pump module are replaced with somehting sturdier.
ECM/engine mgmt- the 2001+ is a OBD II and tricky. Are you running a auto or a stick? Do you plan on keeping all the OEM 2001 electricals? Easiest way is to use the 92-93 ram electrical set up on your 90. In some ways, you're lucky because the 90 will have a VSS, and the electrical speedo plus the abs sensor in the rear end which can double as a sensor for the comp sometimes.
One thing important will be to cut a hole for the crank sensor on the bellhousing