Steering, Suspension, Brakes, Wheels & Tyres
Replies and fixes
Speedo is driven from the differential,
but I'm thinking when you changed the engine one driveshaft was disturbed.
most likely the inner C/V joint isn't fully in,
done it myself before,
~Big hammer and lump of wood and,so as not to feck the inner c/v boot,carefully drive the inner c/v fully home into the diff.
Really doesn't take much for them to spring out of engagement.