Not sure if the reed is any larger, but what you bought was a performance reed material, supposed to be more sensitive than stock. The reed block & manifold will work with a 21mm, but maybe better for a 19mm if you wanted a bit more mid-range power. I run a 150MJ / 20LS in my VM20 Mikki when I use it on my 65cc Metra with a Proma Lowboy.
I've also ran my 24mm Mikki through the same reed block in your pic with stock tin petal and it ran fine, especially on the top end.
I have no experience with Delos, don't know how they compare - jetting wise - to a Mikki.
That said, start with the 90 and you may need to go up a notch or two. Check your plug chops.
Enjoy the mid 40's & beyond