Hi Swalk56 and Dutchy,
It's nice to meet you Swalk56!
49D. Blocks = Anvils
five = v (in roman numerals)
nails + v is an anagram of 'anvils'
66A. Fast = Swift
does it fly fast = swift (bird)
Definition. Swift- A small plain-coloured bird that resembles a swallow and is noted for its rapid flight
Regards, Butterfly