Hi, Ive had the Esky van for about 6 months now, finally done a compression test with some surprises. Number 1 to 3 was 2 at 160 and 1 at 150. Number 4 has 130 but come up to 170 wet. Its a 691M, was by the previous owner a number of years rebuilt but bored out 100th. Can they go that far? I was going to ditch the motor but maybe it may go a bit longer. It is fummy from the filler cap, I doubt its done for unleaded fuel. The bolt ons need work or renew. Any thoughts on this motor or would a 711M be a better option.

If your going for a rebuild with more power you can get the stronger 711 for not a lot of extra $.
Depends if you want to keep an origional spec?
 
Info from Burton power tuning guide for Kent's
 
1970 saw the big change to the thicker-walled 711M block with square mains caps, large diameter followers, wider cam lobes and modified crank seal. Also, the head was now completely flat.
There are two main capacities of 711M, determined by block height - the 1600 is 7/16" taller and you can see the difference between it and the 1300 by the space between the water pump and head. Also, the 1300 has 711M 6015 AA cast in the side whereas the 1600 ends in BA.

I am running the motor until I come across a 711M to replace it, I think I may have found one but it will be a couple of weeks before I can look at it.