The service manual shows how to remove the engine on pages 16-20, but to replace the rings you can do that with the engine in place. I just replaced the rings and pistons in my 1951 Frazer without removing the engine. Keep in mind the cowl extends a bit over the back of the engine block, but it is easily done. I also did a valve regrind while I had the head off. If you are a competent mechanic, you can do the job.