Its a motor with rectangular exhaust ports so must be a Speed Twenty or Silver Crest cylinder head. Reply
An apparently identical picture appears on p21 of the Silver Crest owners handbook,though slightly cropped. Reply
Alvis Archive 
Its a motor with rectangular exhaust ports so must be a Speed Twenty or Silver Crest cylinder head.
An apparently identical picture appears on p21 of the Silver Crest owners handbook,though slightly cropped.