ROP requirements for historic cars

Hello. Apologies as I’m sure this is something I should understand. I’m trying to work out what the mandatory requirements are for a roll cage for a historic vehicle.

I’m looking at putting a roll over bar into a 1958 Aston DB2/4. We want to use it for historic regularity rallies but might also use it for circuit racing or hill climbs.

Appendix K appears to say a ROP is not mandatory but if fitted must comply with the drawings in Appendix K. If we fit one, the type we’d like to fit would be as per drawing 1 - a single main roll bar behind the drivers seats with rearward facing struts.

But Appendix K 1.6.1 says that a larger engined car must have a cage as per drawings 3 or 4 - or 60 (i&ii)? This is quite confusing as the type shown in drawing 60 is the same as drawing 1?

But perhaps this clause 1.6.1 only applies to more modern cars that must have a ROP in the 1st place? So a ROP conforming to any of the types shown would be ok if it’s not mandatory?

Also, how do the ROP requirements for historic cars change if its circuit racing rather than rallies? Or are the rules in appendix K the same for all disciplines?

Any guidance on how to begin working this out would be much appreciated.

Many thanks!
Craig