Does the new foam have holes in the bottom like the original? If so, you'll have to carve on the bottom instead of the top like I did. Hopefully you still have the original to use as a pattern.
I think I'd call CEET first and see what they have to say. Maybe they just made a mistake and sent you the wrong part. I didn't call them because it looked like they didn't have a foam specifically for the '74 available and it isn't a big job to make your own.
Good luck with it.
"Fast is fine, but accuracy is everything"--Wyatt Earp
'09 Electra Glide Classic
'04 Sportster XL1200R