The MGC was a more potent version of the common MGB, substituting an inline six in place of the B's little 1.8L four. You can see the bulge in the hood needed to clear the radiator, which was located further forward due to the longer motor, and the little bump that gives clearance for the dual SU carbs.
The 2.9L BMC C-series six cylinder made 145bhp in production tune, which was a fifty horsepower boost over the four. In exchange for half again the horsepower, though, the car became extremely nose-heavy. Even though the powerplant was a redesigned, lightened version of BMC's existing straight six, it still weighed two hundred pounds more than the four cylinder engine in the MGB (itself not very svelte, being a 350+ pound cast iron lump.)
The MGC was roasted in the British motoring press and only lasted two years in production.
Interestingly, the later MGB GT V8, which used the 3.5L Rover V8, did not suffer from these problems. In fact, the aluminum...well, "aluminium" now, I guess...V8, originally designed by Buick, was actually about forty pounds lighter than the cast iron B-series inline four.
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