I think you are on the right track. The SRM for concentrated stout could be in the 500 range (sounds high), though I think the 81SRM final color is a little suspect (unfortunately there are lots of bad formulas for color out there...you see color gets non-linear beyond about 20 SRM...but that's for another discussion). Stouts rarely run beyond 45 SRM if properly calculated.
The IBU's are probably correct - I would personally match it with some suitable pellet hops (EK Goldings for example) to back out the equivalent amount of hops from the IBU number.
Cheers!
Brad