Dash Nada
Anton,
You are correct sir. I have installed two straight mount "A" or "Dash Nothing" 0-320's in my RV4 and now my RVX. I salvaged them off an Apache many years ago. These engines were common in 1950's era Pipers like the Apache and the early Cherokees. The flange bolts do vary as the hollow crank engines have the 7/16 bolts and some solid crank engines have 3/8 although some were adapted over the years. It depended on which prop was certified for the installation. The lugs are removable and can be adjusted for your purposes. Saber MFG sells extensions with several options to match. Consider using an electronic ignition or P-Mag on one side, it easily gave me 3-5 HP and dropped my FF 1 GPH. The Rotec TBI works well on this engine too which makes it Mogas capable.
Built correctly they are great little engines, lighter than a wide deck 0-320 and can be bought very reasonably. Their only drawback is the case through bolts aren't strong enough to upgrade to the 8.5:1 pistons to make it 160HP. In the 0-320A, the stock was 7.4:1. The local airboat boys run an aftermarket forged TRW racing piston that is 8.0:1, I run the same pistons in mine. I am running all aftermarket airboat racing parts except my crank and cam which are yellow tagged. Good Luck!
Smokey
HR2
RVX