Awkward ideal classic boiler replacement - help pls

[Knappers]

Hi, I'ts been a while but its time to call on you guys for some help and payback with a peppering of advice across the forum.

I've got your typical ideal classic replacement:

• side exit flue
• small high cupboard

Etc.

I'm looking at regular boiler replacement and would normaly go for a baxi 600 or worcester ri.
The problem I have here is the flue position tucked in under/close to the eaves of nextdoors porch.
If I lift the flue (as I guess I'll have to) I'd likely not just be too close to the porch,but would prob hit the gutter.
My go-to move here would be to push a combi in airing cbd, except here we have a 3 storey house with a boilermate stranded in the middle of the house.

I'm thinking will need to be a Vaillant or viessmann with some external flue to clear neighbours porch?

Then there's the boilermate to replace, quite sure floors will be OSB so tempted to replace like for like to avoid extra work involved with going unvented but is that a sound option now as customer is not looking at any alternative heat source....

Any tips of advice would be greatly appreciated,
What boiler would you recommend?

I'm very tempted to drop the work and let a slinger bash one in but I like to think I'm a proper professional and so shouldn't shy away from a little challenge.

 

[ShaunCorbs]

Does the boiler have to go back where it is now ?

Any other possibilities?

 

[Knappers]

It's not easy, house is also a HMO so makes access difficult. I could box in flue through floor above but only space is either existing location or airing cbd.
Also because of 2 showers in HMO she wants to keep a cylinder for hw demand.
Think I might try and quote for a Viessmann 111-w in airing cbd with flue boxed in through 2nd floor and out through roof.
Won't be cheap and may see me pricing myself out while maintaining my professional dignity?