I did something similar back in 2012 for my 1st 100miler though with a 20week gap (and a half IM at 10weeks). I had an ok but not spectacular IM race, though think that was more overcooking the bike. So yes it is doable, whether it is sensible or not only you can say :D

I had one week rest after the 100 before starting some easy cycling and swimming and started running again after 2weeks (short and gentle). Then went into a bike focus until the IM.

I thought you were going to ask about doing IM a couple of weeks after a miler. But almost 4 months, I'm not sure what sort of feedback you're looking for.

You're going to have excellent base endurance fitness going into the miler then nearly 3 months of IM specific training after.

How much time does anyone really need between big races?