The 216 parts will probably bolt on, but they won't be exactly right. The 261 uses a considerably higher-volume carburetor with different bolt spacing at the throttle base, so while the 216 manifolds will fit with some tweaking, you'll be way undersized on the carb with no good way to correct the problem. I think there's a different length pushrod, and the erlier rocker arm assembly has a different oiling system. The distributor will drop in, but the centrifugal advance will probably be wrong - - - -possibly different vacuum advance numbers, also. I'd suggest finding a trashed-out late model 235 as a donor engine- - - -the parts will be a much closer matchup.
Jerry
