Just curiosity but I thought it was assumed no RRS got the engine pre heater as standard. However, my SDV8 Loan Car has no park heating function but definitely has the fuel fired heater. Is it just a case of enabling the software?

If it definitely has the FBH, then it can be enabled, yes.
Are you def sure it has it? It's in a different location on the new style Rrs.
Unless the sdv8 has it and the sdv6 doesn't. The ones I checked were the 3.0 v6 ones. Bodsys Brake Bible
Software Updates Contact me
RRS Timed Heat/Remote kits - Contact me
BAS Engine Re-maps/ EGR Blank EuIII and EuIV
Clock On The Dash/ SNOTM /3Flash / BT Update /Service Reset/Error Codes read\ Gearbox Reset
See it HERE

Can you take a pic? Bodsys Brake Bible
Software Updates Contact me
RRS Timed Heat/Remote kits - Contact me
BAS Engine Re-maps/ EGR Blank EuIII and EuIV
Clock On The Dash/ SNOTM /3Flash / BT Update /Service Reset/Error Codes read\ Gearbox Reset
See it HERE

It 100% has it. I checked topix and it even says: LESS Engine Block Heater

It also mentions the fuel burning heater on the build sheet and I smelt it this morning.

The SDV6 doesn't get it as standard.

Could this be due to the relatively older technology in the V8 compared to the more recent SDv6? 2020 Pangea Green 1st Edition D240 New Defender 110 is here and loving it
2018 Melting Silver Mini Countryman PHEV - soon to be replaced
2015MY Corris Grey SDv6 HSE Dynamic, the best car I have ever owned, totally reliable only a cou0le of rattles in 3 years, now no longer in my care
Also in my garage is a 1996 TDi300 Defender 90 County HT made into a fake CSW

I suspect thats the case, the sdv8 can't get to operating temperature so needs the additional input from the FBH.
So looks like the sdv8 can be retro enabled. Nice one.  Bodsys Brake Bible
Software Updates Contact me
RRS Timed Heat/Remote kits - Contact me
BAS Engine Re-maps/ EGR Blank EuIII and EuIV
Clock On The Dash/ SNOTM /3Flash / BT Update /Service Reset/Error Codes read\ Gearbox Reset
See it HERE