Being the lucky owner of each of these cars, I feel well-qualified to discuss this. I had the opposite problem - good 130, bad 110. I looked into putting the 130 in the 280C and decided to fix the 110.

Comparing the 280C with the 250C:

The intake manifold and carb are on the left side of the 110, not combined with the exhaust on the right like the 130.

The battery is on the right side, not the left.

The 110 has completely different throttle linkage.

The air cleaner plumbing is different

The emissions stuff is completely different and the 110 uses a vacuum pump mounted on the front of the right camshaft to keep it all working.

I am not sure about the interchangeability of transmissions.

The major hassle would be moving the battery. The 280C's tray is bolted in, but you would need to fabricate the mounts on the right side of the 250C. The tray on the 250 is welded in and would be a PITA to remove. There was a swap like this on e-bay and the battery ended up in the trunk.

Finally, the '73 M110 is not exactly the peppiest engine around, especially if you have the 120 hp California version. I would go for either fixing the 130 or finding a used engine. You could probably get a decent one for a few hundred bucks.

Chuck

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Chuck Taylor
Falls Church VA
'66 200, '66 230SL, '96 SL500. Sold: '81 380SL, '86 300E, '72 250C, '95 C220, 3 '84 280SL's '90 420SEL, '72 280SE, '73 280C, '78 280SE, '70 280SL, '77 450SL, '85 380SL, '87 560SL, '85 380SL, '72 350SL, '96 S500 Coupe