My experience, buying any seat cover that comes without the foam to fit that seat cover, is frought w/ fitting challenges, unless one has a competent and experienced motorccyle upholsterer. Even, sometimes, when there is an accompanying foam base available that "matches" the cover, proper fitting can still have it's issues. I bought a Yamiya cover and had my friend who is known regionally for his motorcycle seat upholstery expertise cmake the foam base and he met challenges making his foam base fit the Yamiya cover. Even though the seat came out looking quite nice, if i had it to do over again, i SHOULD have bought the Yamiya foam base for a perfect fit. I have used Yamiya red foam bases in the past and even then, they require "adjustments," albeit minor, for a perfect fit which is achievable. My friend used white foam and since i had the remains of the old red foam base, he used it in the areas of the seat pan's vent holes to give the "red foam look."
As we know, factory original red foam bases were not solid, they were constructed using (gluing in place) vertical blocks and so there were considerable air spaces visible thru the vent holes in the seat pan. Pretty sure, if i remember correctly, red Yamiya foam bases are solid and not constructed using these blocks creating air spaces. If one is to be "hard core" in their foam base restoration, the red Yamiya will not appear correct for original, when one looks at the red foam base thru the vent holes, as supplied from Yamiya.