Majority of F Mk.VIIIs were Merlin 63 engined, and some others had Merlin 63A.
Merlin 63A was the same as Merlin 63, it just had a crankcase from a Merlin 64 that has a protrusion for a pressurisation drive (for the Merlin 64-powered Spitfire Mk.VII’s pressurised cockpit) where the Coffman starter was on Merlin 61. Even though the Merlin 63A didn’t have the pressurisation gear installed, or a Coffman starter AFAIK.
Because they were all built by Supermarine though (rather than at Castle Bromwich where the majority of Mk.IXs were produced), all Mk.VIIIs had the starboard engine panels for Merlin 61/63A/64 with a bulge behind the propeller to ease production regardless of what engine was installed and what Mark of Spitfire the panel was destined for.
Even the LF Mk.VIIIs with Merlin 66, and HF Mk.VIIIs with Merlin 70, where the parallel F, LF and HF Mk.IXs being knocked out in large numbers from CBAF with those same Merlin 63/66/70 engines, had smooth starboard engine panels.
So all F Mk.VIII look like they should have a Merlin 61 with the Coffman starter, even though only the first batches did. But that allowed some of the later ones to have Merlin 63 engines that used surplus Merlin 64 crankcases, as Merlin 63A.