I am not an expert by any means, this is just a summary of the information I was able to gather from searching the web in reference to your question. If any of this info is incorrect please say so, I don't want to pass on ANY wrong advise Hope this helps.

As The rule of thumb is that you can feed prey items that are no wider than the widest part of the snake's body. While Boas will often gladly eat prey that is actually too large for it, they will generally regurgitate the prey item one or more days later. With all snakes, keep the handling of a Boa after eating to the absolute minimum for 24 hours,48 hours is a safer choice. Apart from the possibility of regurgitation, rough handling after a large meal can damage the snakes digestive tract and may prove fatal. If your Boa regurgitates it's meal, DO NOT feed again for at least 2 weeks(12-15 full days) after regurgitation. This is critical recovery time the boa needs to "rebuild" the fluids back up in the stomach.