The smaller A370 (A350-900 size) would require 2 engines of ~85,000 lbs thrust, where the larger A370 would require 2 engines of ~100,000 lbs thrust.
IF no suitable engine is available for the larger model A370, it could become a quadjet.
IF one or more of the engine manufacturers does a suitable 100,000 lb engine, it could also be used on the A380-800R/A380-900.