Yes the Rover V8 does have a reputation for cracks in the block , BUT, I have never heard of this in a Morgan application.
It probably occurs in the much heavier 4x4s like Range Rovers and Discoveries when driven very hard with poor maintenance.
This engine is remarkably tough, it will withstand almost anything you can throw at it as long as it is properly maintained, and the fluid levels are regularly checked.
I would not worry about a modified engine , especially by John Eales, as above Stephen has done 150,000 miles and I have covered 75,000 with ( I assume) a similar set up
Regarding the choice between the +8 and the Roadster , this is a much more complex question.
The more modern design V6 is a much more efficient engine , so the fuel consumption will be much better , the emissions are better so you don't fall foul of the new ULEZ type regulations.
The big negative of the Roadster is the low ground clearance, which is partly helped by a modified sump.
The sound track of the V8 is definitely a cut above the V6 (someone described it as being "the full orchestra")
The only way is to try both and let the right car pick you.
