Intake couplers?

I'm working on relocating the MAF on a swapped truck. It's got 4" aluminum tubing all the way through. The MAF (old round style) has a 3 5/8 diameter on the back side and 3 7/8 on the inlet side. Currently has 4" rubber couplers all the way around and there is a vacuum leak at the back side of the sensor.

Any leads on where to find coupler hoses that neck down, and is it better advised to get a hose a little smaller and stretch it over the MAF or a little bigger and clamp it down??

Thanks in advance.