Mod motor parts do cost more but they have come down considerably. I love the feel of the mod but the sound and grunt of the 5.0. I have a good friend with a blown 351 and it is just nasty, I have another good friend that has a 99+ mod that was cammed and it was sick sounding. The mod is a good motor, just has to have the right parts, just like a 302. A good set of heads and cams for the mod and it will run right with or around a similarly modded 5.0.
Either way, the best bet to swap to 5.0 is to find a wrecked 94-95 5.0 and rob all the parts u can as the wiring harnesses and sensors and all that will either be different or in a different location. Good luck. Would like to know what kind of a PITA it is.