Thanks Lou,
I have a couple of test frames covered and painted with my normal system. I was going to do the raw fuel test and the hold it in the exhaust test but hadn't considered a stain test. I'll make up a frame with lighter colour and see how it goes.
I did have to play around with the head shims and the compression screw length on my 20 Davis head, but now it's working very well and I am very happy with it.
If I was sure that his 46 FX head wood fit my SF then that would be the obvious choice. I know his 40 head will fit my FSR even if he thinks it doesn't, but it's good to know that the RJL head works well too.
thanks for your reply,
Dave H