If I'm in a hurry heat works well if I'm not I find a good soak in fuel works well. All can be done outside no fumes in the house.
If you use Kroil look beyond the safety data sheets to the chemical fact sheets. I have used Kroil for years at work and at home there are some significant cautions in the chemical fact sheets that are not mentioned in the safety data sheets. Some of the chemicals are highly skin absorbable at all temp and when heated are even more toxic if you breath in the fumes. It is the best penetrating fluid I've used but please use it carefully.
For heat I had an old cheap portable bbq I set up outside, the one that uses those 1 lb bottles. 1/4 steel plate instead of a grill, set the motor on the plate and fire up the bbq. I have also used heat lamps and my latest is a repurposed powder coating oven from Princesses Auto. I have seen people ruin a motor with to much heat from a torch so I only use one as a last resort.
For soaking I find the last inch of fuel in the jug is likely to show signs of contamination so I save this in a marked fuel bottle to use as a cleaner/soaking agent. I open up the engine to let the fuel get to the internals and I try and pick a container and lid just big enough for the engine and pour enough fuel to cover the engine. A lid keeps the fuel from evaporating. Usually over time and gently working the parts the engine will free up.
Upon inspection if the motor is worth saving I install new bearings and seals the old stuff I feel is beyond the best before date.