Just guessing here...but I think a 4.3 will need some modding (hacking) to maybe! make it work. Most likely the door liner will have to be hacked or removed and possibly the interior walls will need to be hacked if they have ribs. If the mini fridge has a top freezer, that's a whole set of other probs.
There really is no set size on what will work and what won't. The sanyo 49XX model works well at 4.9 cf w/ no top freezer. Anything smaller and it really becomes a test of wits and skill. Also kegs vary in size, so there unfortuantely is no easy answer to your ?.