The BMW S6 is a tall engine.... which may be a problem. Also the relationship is not really that long in real terms and tbh BMW were only selling off the units they would no longer consider putting in a current BMW model.... so even if we are considering BMW - then given previous form, looking at engines that are already nearly End of Life for the OEM might be more appropriate.... so maybe a 5-8 year old S6 unit from the previous E9X range.
Alternatively - the relationship with Ford is well embedded, I suspect a low end tune version of the Modular Ford v8 which is available via PowerTorque the UK/EU's main distributor of aftermarket Ford engines which Morgan has been in business with for years.
The M-6007-M50A fits this bill and is also the cheapest engine in the modular range at £6k inc US taxes. NB - this is the same retail at the Ecoboost 2l unit!!
https://performanceparts.ford.com/part/M-6007-M50A
