Camvac Cyclone inlet

I have an old Record Power CamVac vacuum unit (care of a certain online action site) which has a direct entry 4" inlet hose.

I'm using the 2 1/2" dust hose from record in my workshop so began by looking for an adaptor from the 4" inlet.

It then occured to me that I could convert the old style CamVac into the newer cyclonic units so I drew up this adaptor to do both jobs.

Im not sure if the tube needs to protrude into the body so drew up one model with and one without. Id be interested to hear of anyone's thoughts as to if its needed or not.
I made the unit 150mm tall as thats the limit of the height my printer will do but it could have done with being taller to cover all old mounting holes (look in pics) I just put the other bolts back in to close the holes.