Port my Eddy's or Stroke to 408?

Your 4" kit will not use teh B&M flexplate, unless you pay to have it balanced that way. You can do a stroker, but I tend to agree with the guys... You already have a 3.58 stroke, and you will be running the squirt. until you're ready financially, or the 360 expires and tells you it needs to be replaced, I'd spend some coin on the heads and run it that way. The 4" build will change a lot of things, so your convertor and carb/intake will need to be addressed then too.