G. Having checked a 1973 Turbo 310 POH (pre GAMA format) it states that the limitations are in KCAS as are the colour markings on the ASI. The speeds shown in the performance section for take off, climb and landing are KIAS. The cruise performance tables are of course KTAS.
On a Reims F406 the limitations are shown in a chart listing CAS and IAS and over the full range there are only two points where there is a maximum of 1k difference. The limitations and the ASI show only KIAS.
Many of the older singles and twins whose design originated in the 50s and 60s and were built by many different companies had very low normal operating range, flap and gear limitations that do provide problems in integrating with faster traffic patterns.
I was on duty when an operator who had a fleet of Aztec aircraft with some ASIs displaying mph and others Kt. An 80 mph approach to minima and go around led a stall and to 3 deaths. The pilot normally flew another one where the ASI was in knots. The CAA would not permit the operator to change all aircraft to a common standard. Reporting deaths to loved ones and business colleagues one after the other is not a task I would like to do again.