You may find that the drop in bobbin model machine causes tensions problems during FMQing for you and can be part of the thread breakage problem you're experiencing. I've put vintage machines on a frame, but I always used horizontal bobbin machines like a 301. It will also not be much fun to change out a bobbin with a quilt on top of it. The horizontal type are much easier to switch out bobbins. That's why long arm machines are engineered with horizontal bobbins. Better tension control and easier to change out the bobbins.