The Sparrowhawk mod replaces a 2550 rpm prop (McCauley) with a 2800 rpm legal prop (Sensinich). That buys you 5 hp without doing the engine mod, which takes the stock 110hp to 115hp. The rest of the Sparrowhawk mod is to exchange the pistons with high compression replacements that get you another 10hp, thus, possibly equalling 125hp, all from the origional Lycoming O235L2C engine.

I've got a 1978 aerobat with the prop mod only. It has a Garmin 430 in it, which is about as glass cockpit as a 152 can get.