I can’t find anything telling me to preheat the meat before I put it in the jars. Should I heat the meat or pack it cold?
I looked it up in my "Ball Blue Book of Preserving", and it says to simmer meat in water to heat throughout. Pack hot meat into jars, leaving 1 inch headspace, cover with cooking liquid, again leaving 1 inch head space. Remove air bubbles. Adjust two-piece caps. Process pints 75 minutes and quarts 90 minutes at 10 lbs pressure.
Our home economics county agent said she often would take meat out of the freezer and can it, so it shouldn't be a problem, in answer to your first question.

Swifty