Different correctors are usually extremely sensible to the distance between the corrector itself and the image sensor. When using a corrector not specifically designed to a particular telescope this distance might be needed to adjust to achieve the best results.
The T2 or M48 sized adaptors have to be placed between the bayonet adaptor and the corrector. The distance can be adjusted by using different number of adaptors.
M68 distance rings are compatible with 2,5" 0,75x Riccardi reducer.