With the Lokar, if you can access the trans to fill otherwise, fill roughly almost full then use the stick tube for measure. In the past I have drilled a fill hole and added a fill hole and tube to the case, like they do for vans and RVs for motor oil. Drilling in the right place and having one of those push in and lock down plugs will keep the oil in and not predetermine a spot for a crack. You would do it while building the case of course.
Aside from that, one of those fluid exchange machines that hook to the cooling lines would work too.
