Mike,
A whole array of questions come to mind. Do you have a way to post some pic.'s? Without seeing it 1st hand, there could be a lot of useless speculation.
Is this CAT-1? Then, the first, and most basic question; Is the 674 Rototiller spec.'ed to be I-Match compatible (i.e. 26" minimum between lower lift hooks and 16" vertically from there to upper lift hook)? My I-Match is actually 27 1/2" C/L to C/L between lower lift hooks and 15 1/2 from there, vertically to the C/L of the upper lift hook. It works great on my "I-Match Compatible" RB but, I'm not having as much luck making it work with my 1060 GM with the "I-Match Compatible Conversion Kit".
Tom