I can certainly understand the questions around whether the UK could afford F-15Cs; I can imagine the penny-pinching Defence reviews would probably have lead to second hand A/B models being purchased from the USAF if the Tornado ADV was cancelled, if the Eagle was considered at all.
This leads me to think an earlier POD may be needed, specifically with the F-111K. Should this order not be cancelled, this should butterfly away the all UK Tornado variants (GRs & Fs), the SPETCAT Jaguar & RAF Buccaneers at the very least, with the TSR-2 & AFVG cancelled as per the OTL too.
This would certainly leave the UK more reliant on US equipment, but I personally don't see that as a disaster (IMHO) & could certainly save money in the longer term.
Certainly the UK should continue with the Harrier & S/VTOL route, ideally with contracts with the US similar to the OTL that their forces will be customers for such aircraft. Personally, I'd like to see the Harrier II / AV-8B never happening & "replaced" by a supersonic Harrier variant or the P. 1214 / P.1216 jets.
However, I'm aware such contracts may not be honoured, as with what happened in the ASRAAM / AIM-9X scenario so perhaps some wishful thinking is present here.
1970s RAF combat aircraft:
English Electric Lightnings.
F-4K & F-4Ms AKA Phantom FG. 1s & FGR. 2s (with Speys if only to learn the lesson that trying to re-engine US jets can be a time-consuming & expensive undertaking).
F-111K replacing V-Bombers & Canberras in the strike role.
Harrier GR. 1 / 3s.
1980s:
F-15C / Ds to replace Lightnings & eventually F-4s. The RAF will probably want a D variant model with a WSO station in the rear seat. The Eagles are designated F. 1s & T. 2s in British service. They're modified with some UK avionics, Skyflash missiles plus probe & drogue refueling capability.
F-4s slowly being phased out by the end of the decade; F-4Js / Phantom F. 3s never bought due to Eagle order.
Supersonic Harrier II / P. 1216 variants replacing the Harrier GR. 1 / 3s RN FAA Sea Harriers.
F-111Ks with incremental upgrades. Order for F-15Es placed in the late 80s to replace the Pigs.
1990s:
F-15C / D Eagles with incremental upgrades such as AMRAAM, leading to Eagle F. 3s. RAF Eagles deployed to the Gulf during 1990 for Op Granby.
F-111Ks being replaced by F-15Es AKA Eagle FGR. 4s. I have doubts that these will be ready in time for the Gulf War though so the Pig will be sent instead.
Supersonic Harrier II / P. 1216 variants incremental upgrades; also deployed to the Gulf.
2000s:
I'm leaning towards the UK never joining Eurofighter (if it even happens due to the prior butterflies) & instead stick with US jets.
Strike Eagles upgraded to FGR. 5 status with the latest avionics & "smart" weapons - Enhanced Paveway, Storm Shadow, Brimstone etc (or US equivalents like LJADM, JSOWs, SDB).
F-15C / D Eagle ASRAAM & avionic upgrades - perhaps AESA radar & Meteor missiles.
RAF Fifth Gen fighter procurement: in an ideal world, RAF F-22As would be bought to replace Eagle Fs. However, due to the technology involved & the cost, this is probably not realistic.
Instead, the RAF's mixed Eagle fleet will start to be replaced circa 2020 with a mixed F-35A & F-35B fleet. The Lightning IIs will also replace the P. 1216 jets for both the RAF & FAA.
I'm also leaning towards, due to the cost of the high end aircraft all mentioned above, to the RAF getting a more operational Hawk variant. Perhaps HM Treasury during the 1998 SDR, after seeing the upgrade costs to the Eagles & the prices of Lightning IIs, forces RAF to reduce those orders to procure a fleet of cheaper aircraft. These could lead an RAF Hawk comparable to the Hawk 200 series. This could actually be beneficial for COIN work during Afghanistan & post-invasion Iraq where higher end jets are realistically overkill.