sed to cp lines x->y from 1.txt into lines a->b in file2.txt

I have one base file, and multiple target files-- each have uniform line structure so no need to use grep to find things-- can just define sections by line number.

My question is quite simple-- can I use sed to copy a defined block of lines (say lines 5-10) from filename1.txt to overwrite an equally sized block of lines (lines 25-30) in filename2.txt.

Put another way, I have file1.txt that looks like:

AAAA
BBBB
1111
2222
3333
CCCC

and want to copy the lines with numbers into similarly formatted lines with numbers in file 2 (but not with matching starting line numbers).

DDDD
EEEE
FFFF
GGGG
4444
5555
6666
HHHH
IIII
JJJJ

I have been able to do this within an individual file, but haven't been able to bridge the two.

what would be the desired output based on your sample input file?

DDDD
EEEE
FFFF
GGGG
1111
2222
3333
HHHH
IIII
JJJJ

nawk 'FNR==NR {if ($1~"^[0-9][0-9]*$")f1[++n1]=$0;next}$1~"^[0-9][0-9]*$"{$0=f1[++n2]}1' file1 file2