I think you may be are being a bit too cautious. If you alternate tightening the tank bolts, the tank and bowl should come together, but it will take some pressure with a wrench. I don't know about plumber's grease, but do not use silicone. Now as far as the 14" rough-in, have you considered one of the toilets that use the Unifit adapter? I believe there are 3 models that use this, and that would put your toilet in "normal" position. If you get the tank and bowl seated properly, I don't think there is great danger in breaking it, my Drake and Dartmouth are sitting on exactly 12" rough-ins, but still have 2" or so space behind the tank, and I don't see how 2" more would create any more risk of breaking, but the extra space looks kinda hoakie.