According to some preliminary measurements I've made, it looks like I might be able to make a 261 cam fit a 216 by changing the diameter of the bearing journals. I've got a junk 235 cam in the lathe right now to test the theory. If it will slip into an old block I have once the journals are reduced in size then I can do a timing and lift check to see if there might be any piston/valve problems.
Update- - - -with the cam bearing journals resized, a 54-up full oil pressure 235 big-journal cam fits a small-journal (splash-oiler) 235 block and the crankshaft clears everything. Since the 235 has a longer stroke shaft than a 216, logic suggests the same modification would work on a 216. I'll probably pick up a new Elgin 261 grind cam and incorporate it into the updated 216 I'm working on.
Now, wouldn't it be impressive if a 216 can be built to outperform a 235, either in HP, torque, or maybe both?
Jerry