Yep, there are LOTS of conversions out there around 100HP. How about those around 300HP, like LooneyBird is querying us about? George Morse converted a Corvette engine for his lovely Prowler Jaguar
and Geswender's big block Ford's were quite nice, but they were all so long ago, as was FEW's V-8 for their wee P-51. The Mazda conversion gang could at least help you out with an appropriate PSRU design. What is Thunder Mustang using for power?