Swap from LA 273 to magnum 408 water pump and cooling

I can't say for sure but I believe the front of the block /heads and the later up to 80 something use the same timing cover. (69 down use a different timing cover.) And there was a change making the front seal externally replaceable. But if you have all the accessory drive parts and the front cover from a 273 and a cast iron water pump, it should bolt on and fit correctly.

What year is your 408, and does it have a fuel pump on the pass side and standard type intake, not the magnum type of the 90s