Kettle Engine Porn!!!
I did find this interesting site:
http://kengine.dvapower.com/
Toward the end, a dyno graph shows about 245 bhp from a 1.7L, presumably full race spec. Uhhmm, that scales down to 144 bhp @ 1.0L . . . . . . . . . 
BTW, those numbers are rear wheel bhp . . . .
NewlyconvertedtothechurchoftheRoverboy
One more foray into dreamland before going back to the reality of the 5 port BMC head . . . . . . . .Concentrating only on potential output and ignoring cost for the moment . . . . . .
After building dozens of Cosworth BD derivatives over the span of my career, I would estimate that a 999cc K16 Rover with EFI would have an output in the 140/145 bhp range, (Fw bhp) running with an 8,000 to 10,000 rpm rev range.
Building that engine to a "softer, more reliable spec", I would estimate that a "first try" should net 125/130 bhp (Fw) running a rev range of 7,000/9,000 rpm.
The point of this idle chatter and lack of "brevity" is that: even at 125 bhp the K would outperform the best 1000cc 5 port BMC. The best number reported has been 108 bhp, done by "someone" and reported back to David Vizard, etc, etc. I've seen 106 bhp from a 1098 short stroke, so depending on the dyno, 108 from a 1000 might be just possible. But let's use 105 bhp because that seems to be sensible and just at the limit of what might be achieved.
At 95.1 Fw bhp (550 ft. altitude) MM achieved 118.7 mph. So then, using numbers from I/O, Sumner, Woody and Bonneville Pro, and factoring for increased bhp we get:
At 105 Fw bhp: predicted
potential top speed ~ 122.4 mph. Which would be a new record, presuming it could be backed up, etc, etc.
At 125 Fw bhp: predicted
potential top speed ~ 130.2 mph. Pretty speedy for an 80 inch wheelbase . . . . .
The whole point of this is that:
NO 1000cc BMC 2 valve, 5 port, is ever going to produce 125 bhp, AND, have the reserve potential to produce another 15/20 bhp the way a K16 would be able to do.
So what's going to happen? Probably nothing for now. Not my call or wallet.
But, just like every good pilot wants a backup plan that includes a parachute, this is MM's backup plan. Seems like a good one to me.
And now, back to the technology of the 1930's . . . . . . .

(Where did I put that flux capacitor?)

Fordboy
Thanks to Interested Observer, Sumner and Woody for the help with the math, and more importantly, the experience to know what is reasonable.