I did my old '6 using Hammerite spray gloss black (smooth)
I did it with engine in situ - good cleandown, get rid of flakey bits, wash, dry, abrade, degreas.....then meticulously mask off all the "non black bits" e.g. the carbs - that took bloody ages...then spray away little at a time - used 2 and a bit cans.
It is not marketed as heat resistant but it is - I've used it on the downpipes in the past too (smell a bit while it bakes on)
It looked mint but I guess some of that is down to how long/ho much care you take doing it