David,
You hit the nail on the head…many people were employed as a result of the ADV. The GR1/4 was a superb aircraft – optimised for its low level interdiction role, though the central european mission did leave it a little short on legs compared to, say, the F111. The F3 on the other hand was a massively compromised fighter that arrived without a functioning radar, no auto wing sweep and a severely curtailed operating ceiling compared to the Lightning/F4 (even Hawk….). At the very end of its service life the F3 finally had a credible capability with ASRAAM/AMRAAM (though not a perfect integration…) but still suffered from a sub-optimal airframe. It was very fast at low level…but then it was designed as a low level bomber. Fighting an F3 after fighting a Typhoon was always a bit of an anti-climax…Yes it was wrapped up in Al Yamamah, but the Saudis bought F15Cs too. As a bomber killer the F3 served a purpose and, on its day, with JTIDS/AMRAAM/ASRAAM could spring a surprise, but it was never a ‘pure’ fighter and the F14 would have fulfilled the requirement better (albeit we’d have struggled with the TF30 engine too….).

No, the Brits would have simply substituted the Spey (both were early 1960s engines).

The Spey was slightly smaller than the TF30 and had similar airflow requirements and identical thrust (the F-14’s TF30-412 compared to the Phantom FG.1’s Spey Mk.201), so there would be no repeat of the Phantom fiasco.

TF30-412: thrust 12,350 lb (20,900 lb reheat), weight 3,969 lb, length 125” engine/235.5” with tailpipe & reheat module, diameter 42.06” (50.90” over reheat module), SFC .63/2.78 in reheat, Airflow: ~240 lb/sec

Spey Mk.201: thrust 12,250 lb (20,515 lb reheat), weight 4,093 lb, length 205” with tailpipe & reheat module, diameter 37.5” (44” over reheat module), SFC .63/1.95 in reheat, Airflow: 210 lb/sec

Of course, they could fit reheat to the RR/Allison TF41 (improved Spey) of the A-7D/E, which would give 15,000 lb thrust dry and likely ~24,000-25,000 lb with reheat.