Assuming a 5.9 as opposed to a 5.2, a couple of things come to mind.
-Don't limit yourself to the '97 and up Magnums. The later ones came with a one-piece damper/pulley, which you won't be able to use with your LA front drives. Stick with the earlier (~'98 and earlier?) units that have a separate pulley and damper, then your pulleys will bolt right up (need to oblong one bolt hole on crank pulley).
-Make sure you get the flexplate with your motor ('95 and up) as it has the external balance weights that will allow you to use your internally balanced 904 convertor (early OBDI motors had a neutral flexplate and used a balanced convertor). If a 5.2, no issues since it's internally balanced. Oblong one hole and the convertor bolts right up.
-Consider getting the cam ground on an LA roller core instead of a Magnum core- then you won't need the eccentric adapter from Hughes, since the LA roller cams all had the long snout to begin with. The adapter can be a little janky to install, but sometimes it's your only option.
-Add a heater hose/bypass nipple kit to your list. Beats the heck out of trying to wrestle the 55 year old fittings out of your old manifold.
Mancini Racing Small Block Heater Hose Nipple Kit
Make sure you get the one for early LAs so you have the correct 3/4 bypass fitting to match your water pump. Since the manifold is cut for the later, larger 1" fitting, you will also need a reducer bushing for the nipple to correctly fit.
-Mod your existing throttle/kickdown brackets to fit the Magnum manifold.
Throttle Bracket for Magnums
-You didn't mention your plan for carburetion, but whichever carb you go with make sure you also get the correct Mopar throttle/kickdown adapter.
Edelbrock Throttle Lever Adapter
