Currently, I'm in the process of building a 258 cubic inch inline six on a 216 block that will look exactly like the original engine in your truck. Even the casting numbers will shout "I'm a 216"! That project isn't easy, not inexpensive, and there are very few machinists who would attempt the project, even with an unlimited budget. My first one is headed for a demonstration trailer with a dyno attached, and it should get some attention at car shows.
If you can find a 261 engine to build, that will be the simplest, and probably least expensive way to stay original-appearing to most of the people you'll encounter at a "show and shine", especially if you use the 2-bolt valve cover off the 216.
Jerry
