try some penetrating spray. mine were rusty but i just used a right sized philips head and it came right out.
Anyone wishing to aspire to such engine beauty in their own cars, should think twice about getting a jetwash in there & blasting the cr@p away...
If it must be cleaned clean it by hand with a good engine de-greaser & paint brushes, but as an extra caution, put some water resistant covers on ALL the electrical connectors under the bonnet, or you could well be back on here asking how you get the car started or fix a poor runner!
your engine bays look so good painted,have you just painted stuff with a brush or removed it ?