I won't address the question of whether an auto conversion is cheaper/more reliable/safer (or the converse) than an aircraft engine, but I will address a couple of issues with your other claims. While SB's are not mandatory, AD's are (for TC'd aircraft, and for EAB's specifically listed in the AD), and at least for Lycoming engines, there is at least one AD (2004-10-14) that requires an engine inspection in the case of a prop strike. Lycoming's definition of a prop strike is VERY broad. HOWEVER.... This is NOT correct. AD's ONLY apply to E-AB aircraft if the aircraft in question is specifically called out in the AD. And since an engine is not certified unless it's using a certified engine/prop combination, there are very few E-AB aircraft that will have engines that are subject to AD's. Now, I tell all my customers that if an AD is issued on a certified engine, and if their engine is a derivative of a certified engine and uses the same component that is discussed in the AD, they should seriously consider complying with the AD, but it's not mandatory. So, with respect to prop strikes, if your engine meets the criteria for a prop strike that Lycoming calls out, even if you're not subject to the AD due to your non-certified O-360 (or whatever) engine being in an E-AB aircraft without a certified engine/prop combination, you should seriously consider a tear down. I don't see an auto engine/PSRU being different in this regard - if the prop touches the ground, you're going to need to tear down the PSRU and MAYBE the engine, depending upon the PSRU type.