The easiest engine option for the Loaded dice is defiantly the OS140RX.
with anything else, the amount you have to cut out of the very slim and tight cowl for mufflers or wrap around headers makes it a difficult model to work on. It was an early 2M model, and has a skinny fuselage, and as such the 140 has a great power to weight ratio, and is still very competitive.
The other advantage, is it is pumped making the fuel tank location over the c of g, which is again just a lot easier to service than one that has to be stuck right up against the firewall! basically, the 140 rear exhaust motor option would give you the best Sports model on the field, and with all the pattern pilots going electric, second hand OS140's would be cheap too, after the first start of the day, they are usually started by just flicking the spinner backwards, a brilliant motor!