273 or 225?

If you swapped in the 273, you might want to hunt down a pair of 67 of later heads because of the intake issue. Another thing to consider is the earlier 273s had a smaller crankshaft register than the later ones. Something else to consider as mentioned earlier is get a 5.2 or 5.9 and build everything on the V8 K member while you are driving the slant around.