I have removed and installed main bearings by putting the case half on a pair of upright concrete blocks, and used a small propane camping heater underneath the case half to heat it up.
It takes a while, but if you can spit on it and it boils, you are getting close.
Take a wood drift and a mallet, and try to tap the bearing out. If it's real stubborn, keep it on the heat longer.
Once you tap it out, then you can use oven mitts to turn the case half up so the bearing seat is seen, and then drop the new bearing in quickly and accurately, and it will very quickly be held in place by the shrinking bearing seat in the cooling case half.
Then do the other case half.
I've done this a few times. Just clean out the case halves real well before doing it, and try to keep it clean. You can do it in the workshop, and try not to get any dirt on it.