Andrew I have a 1700 SS Xflow and had a similar issue, nearly drove me mad. Replaced everything you had done and even had a hole drilled in the fuel cap in case of an airlock. Problem eventually traced to dodgy igniter in the (Aldon) distributor...worth a look. My car would run fine for 10-15 mins then same issue as you, refused to go past 4k revs, die and then 20 mins later run fine Thread can be found under 'XFLOW WOES - FINALLY SORTED'. Good luck