Mark,
You could do both. I’m also restoring a speedster at the moment - 83103 - and will be running a 912 with 1720cc but also building a period correct engine to keep on the shelf. My car’s original engine was 64903 and I recently acquired 64930 from Ron Sieber. Funnily enough, Ron was about to put a similarly close-numbered engine in his speedster, having run it with a 912 engine for some time. Seems we all wrestle with the same question!
Phil
Phil Parry
Essex, UK
1960 BT5 110563 RHD
1954 Pre A 1500s 1953 model year (project)
1957 Speedster (project)
1972 Original unrestored VW camper