Thank you Bkay. It's encouraging to know I can do a pretty good job on a 201 without needing a metalworking workshop. I think I'll try to steer clear of 66s unless/until I start to consider myself a bit of an expert at this caper!
Yep, I've done the straight-needle, insertion correct check list. The throat plate is a vintage Simanco part - but that's no guarantee it always belonged on this machine. If all else fails (like the suggestion of the area to clean from LeonF) then I'll look at comparing to another throat plate just in case the needle alignment is totally perfect and I've got a dodgy hole.