It's a gamble where yo could control the odd's ?
I'd prefer a Service history, as this tells the cars story. These V8's sludge up so do need an oil change every 6 months. D2's are high maintainence ( as we know) so its crutial to know what's been done and when all the other fluids have been done, repairs etc.
If the one with 81k's has been maintained and serviced fully, albeit cosmetically the body is messy, i'd live with that option IMHO
If the heads have just been done on the other then it overheated! Did the radiator get serviced/replaced?, new thermostat , viscous fan, hoses? was the block checked for cracks?. If the heads just got done then perhaps lack on care let it fail?. After all heads don't just go for no reason. Like slipped liners. Both these issues are not failing's in the V8 they are the fail's caused by other problems.
If it helps , no history is a gamble.....My friend took the same gamble with a 2006 D3 which had little to no history. We even called the LR dealer which stamped the book at one point who had not seen the car back there since 2009 while. LR checked it over and said all OK. 20,000k's later the Auto Failed as it had most likely not been serviced , 7 grand out of pocket. Hind site maybe should have had the Auto Service the day he bought it...