The only diesel conversion I've done is on a OS FP25 many years ago, so I don't know what a big one like that would do. My impression of diesel conversion is that you do get a little more power and burn a little less fuel, but it wasn't a significant change - certainly not the "doubling of power" that some vendors claim.

I didn't really like the diesel operation. It lacks the tweak-the-needles-and-go user friendliness and simplicity of glow fuel operation. Settings are finicky, and it's difficult to keep the fuel fresh for long periods of time. What killed it for me in the end was the availability of model engine diesel fuel. Do a search in your area for a good reliable (and hopefully cheap) source first, before you contemplate the idea any further.

There is a reason RC gasoline engines are enjoying a phenominal growth. Pump gas is cheaper than bottled water, and you can hit 12 gas stations on you way to the field. I recently bought two World Models 1/4scale Cubs, and IMHO gassers are the only way to go. Anything from 20cc-40cc should give power to spare on a Cub. I do have big glow engines but I would only go to those if I need maximum power-to-weight (e.g. 1.20 class aerobats).

BTW, that 1.48 should be plenty power for that 1/4 Cub. I would imagine you could fly it around at 1/4 throttle all day long. One way you could save money is by going to lower nitro content. I'm sure 5% or even FAI would be just fine for that application.