Converting an M103 engine to carb would be a monumental task and I bet it would not even run properly or would get horrendous mpg's. I would not bother. Unlike the Earlier M110 engine it was never designed or intended to be used with a carb.

The stock fuel system is not all that complex, its just touchy. On the 300E the fuel pumps are hardly ever the problem with a poor or non running engine.

Another alternative would be to find a diesel engine to stick in there, like an OM602 or 603

Or if you want carb I think there was a rare version of the M102 engine that was carb....way more trouble than its worth though. I'd go diesel.

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