phrases - Word Choice: Starting a sentence with "If not too long ago"

I know that the proper way to use "not too long ago" is: "Not too long ago, contractors used to build houses and sell them to dealers. It was the responsibility of the dealers to provide financing to potential home buyers."

Instead of these two sentences, can I use:

"If not too long ago, contractors used to build houses and sell them to dealers, who were responsible for providing financing to potential home buyers, today most builders also offer financing alternatives."?

My question is whether "if not too long ago" is correct or not. If it's not correct, I would highly appreciate it if someone could explain why.

Thank you,

Maria