Neither one is an easy swap, but the 409 would be MUCH more difficult due to size and weight, particularly the width of the engine with those huge heads. Find a driver's side exhaust manifold for a 265 with the front outlet to install on the 283 and it will give you some much-needed clearance around the steering gear on the driver's side. Even with that manifold, the steering gear might have to be moved a little.
Jerry

"It is better to be silent and be thought a fool than to speak and eliminate all doubt!" - Abraham Lincoln
Cringe and wail in fear, Eloi- - - - -we Morlocks are on the hunt!
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