The diameter of the original 5.50x12" tyre was 552mm. If you can keep the front tyre size reasonably close to, say 565mm or less, you should have no problem there, but lesser is better, down to about 550mm.

A 5" or 5-1/2" wide rim will work well with a 185 width tyre & if the backspace of the wider rim is very close to 4-1/2", you should be fine.

As for the rears, then a 195 width tyre will be good & a 205 will be pushing it if you have rear seat passengers, but OK if not. A 5-1/2" rim is good with the same backspace & a tyre OD of somewhere close to 575mm should give no reason for grief.

Personally, I wouldn't go for the 16" but as someone keeps reminding us, we are all "individuals", so if you can make it work, then go for it.