It appears that you do have the correct tag, I used the numbers you provided and they came up different.
"Tag of the driverside door frame just has - (FP-H 6586)"
Be prepared when you go into the DMV. Explain that you want to register the truck using the body tag on the door pillar. Explain that the original engine has been removed and the new engine does not have the same numbers as the registration. Take any info you have with you.
