The only plain bushing split case I'm aware of would be the MK1 VA engine. These may have been the lightest with a slight edge over a good running TD. The MK2 was a solid casted case. The MK2 was superior to the one but didn't come without problems. The conrod attached to a landing with the wrist pin the screwed into the underside of the piston skirt. Although ABC construction, both engines should be used with a 20% castor oil fuel due to this assembly which is known as a gudgeon pin. Both versions had this and it was used in conjunction with shim spacers to alter the timing. It sometimes would come loose which wasn't good and really needed to have Loc-Tite installed in the threads. The wrist pin would also develop play in the landing area of the threaded disc . Both models are no longer produced and generally fetch a pretty high price. The MK2 NIB usually sees prices nearing $100 or more dollars on the examples I've seen on Ebay. Ken