I have a heidt's in my 39.
I bought a disk to disk kit, a bit pricey, but all NEW components. The only isse i had was they sent the 2 inch Drop spindles, vice the stock height that i asked for...
The most important parts of the installation is MEASURING and MARKING!!
Mark the centerline of the front axle. Measure, cross-measure and remeasure everything about 20 times. Then have someone else do the same.
I hired a welder for a day to do the actual welding in, which was a good move, as my welding skills leave much to be desired...
The welder also measured everything twice before starting to weld everything in... it took about 7 or 8 hours including lunch and a few breaks.
The truck drives down the freeway 80mph+ with no dog tracking or wandering.
