It might be helpful to post a pic of the current motor and clutch system . I think you are going to find that a servo will be the fastest and easiest way to go , all that is required to mount it to the table is to drill 3 holes thru the top of table and put in 3 carriage bolts , there is a lot of adjustment (slotted mounts on the motor ) so the holes don't have to be dead on . I bought a 111 on an old USM table and it has a similar set up as you have described and its not to hard to convert it over to a servo which I will do when I have time to look over the machine . Where are you located ?
If you cant just drill the table because the old mount is in the way and can't be unbolted then put up some pics and we will see what we need to do , don't get to frustrated Im sure there is a fix (wish I could take my own advice LOL ) If you need help with an adapter plate I can help you with that as well ..
A side note on the servos , I am new to all this as well and did a bit of research on the servos before I bought one (after it was recommended by a repairman in NC ) there are cheaper servo motors available BUT the one that Bob sells is the only one that I have seen that has built in gear reductions and what I have been told is that some of the others don't have the same power at very slow speeds (they don't reach rated output at low speed ) .... The servo motor is a totally different animal then what you have now , they don't run all the time , they work just like a variable speed drill (best way I could think to describe it ) another up side is that they only draw juice when you are sewing ..