Hello,
I assume you used new streach bolts as these must be replaced when you do the head.
Another thing is that the bolts need to be torqued up loads. My mate did his head and I think you tighten them to a setting and then do one complete rotation, he had to use a scafold pole to extend the wrinch to get them turned so its a big old job.
If its not that then it could also be a valve, worn guide, bent etc?
Unless you have all the kit, space time and knowledge, new rings could be tricky. With a K-Series engine going for about £500 then id go for a new engine. Why not go all the way and got for a modified one with 135 bhp or something?