6945 is the first with the updated engine, it has bigger intake valves and an extra coolant passage. If you use a coarse mazed radiator from an earlier, or a later model, the engine can easily take turbocharging.
The connecting rods are the same as the later 7745 turbo, which was 90hp. This one however had hardened valve seat inserts and a gel headgasket. I'd say it will last quite a while at 75hp, if you want more you'd need the whole package. And an oil cooler.