Yeah, I did the AC amps calculation and came up with 10 amps to power a 1000 watt heater with a 1000 watt inverter that's about 90% efficient. What I forgot to do was the DC half of the equation. To convert 1000 watts at 12v DC up to 1000 watts at 110AC takes about 90 amps DC current (stepping the voltage up on the AC side by a factor of almost 10 requires stepping up the current on the DC side by a factor of 10 as well).
Maybe a second battery - a BIG marine battery - hooked up in parallel with the car's starting battery is the answer. An 80 amp-hour battery will (theoretically) supply 80 amps for 1 hour. If a 1000 watt block heater for 1 hour will do the trick, then it would work. Maybe a 500 watt heater run by a 500 watt inverter for an hour before starting it in the mornings would be a more reasonable plan.

Of course your 55 amp alternator would have to be running at its max output for about an hour and a half - with no other current loads so it all went back into the battery - to fully recharge the marine battery with the 1000 watt setup. With the 500 watt setup it would only take about half as long to recharge, or half as much current from the alternator.

And just think, an 80 amp hour marine battery can be had for ONLY $200-$300...

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1984 300 Coupe TurboDiesel
Silver blue paint over navy blue interior
2nd owner & 2nd engine in an otherwise
99% original unmolested car
~210k miles on the clock

1986 Ford F250 4x4 Supercab
Charcoal & blue two tone paint over burgundy interior
Banks turbo, DRW, ZF-5 & SMF conversion
152k on the clock - actual mileage unknown