Erm SSL is not obsolete... however I know how you meant that so just a

for you lol.
Try this:
https://vborg.vbsupport.ru/showthread.php?t=276547
As for SSL in vbulletin it should be a simple matter of setting the BBURL to
https://yoursiteurl.com/forum etc and that's it, re-captcha should work fine I was just on a https vbulletin 4 forum and no changes were required so not sure why you're having troubles.
Edit: Although to be fair on that forum I do not believe they use re-captcha so editing may or may not be required, if someone has more insight on this please share as I have not looked into it in-depth at all.