Sorry, I know awk/sed was requested, but a python solution was so easy, couldn't help to post it:
#!python
(a, b) = ([], [])
(i,j)=(1,1)
diffchar=['.',':']
for line in open("sq.txt"):
line=line.strip()
if i == 1:
a = list(line)
elif i == 2:
b = list(line)
elif i == 3:
for (x,k) in enumerate(list(line.replace(' ',''))):
if (k in diffchar):
print a[x]+str(j)+b[x]
j+=1
i=0
i+=1
Discard if you can't have Python. This may give you some idea about the awk code though (feel too lazy to translate in awk:)
HTH