A D&B 3.7 would probably fit OK--the problem is the spark plugs point up on the twin-so they are really sticking more out of the top of the cowl than side-If they pointed toward the rear of the engine, it would be no problem--also at 5.4 lbs W/ignition it may be a little heavy, but not much more that a G62. A quick thought on the prop if I may add--I was running a PK Plus 22/8 on my Pitts with the Taurus 52. I also tried a Mejslic 23/10, Zinger Pro 22/8, 22/10, and a Biela 22/10. Personally, I found the best performance with the Belia, and PK Plus and oversize Mejslic. It kept the RPMs in the low to mid 6000-(which most people say is not enough) but the performance was spectular. You can get more revs with other props, but for me, I found it is performance and not RPMs that count. Bill O agreed with me. He says the peak performance with the 3.2 is in the 5800-7000 RPM range. Just my opinion of course.