Okay, I have to catch up a little here.
The exhaust leak will need to be fixed. We have methods for this.
And that finned exhaust "clamp" is nothing more than a visual accessory. It never came with the bikes, and it doesn't do anything. Some people like the looks. You can leave it off.
But for now, we need to to do a wet compression test, to see if the low compression reading is from valves or rings. You have a 60psi figure now, which I assume was taken with a few crank-overs with the throttle WIDE OPEN. That is important.
Normal compression on the regular Iron Barrel Bullets is around 110psi.
So, then we read that you have oily plug and stuff, and low compression, so we want to see if it's rings or valves. Take out the spark plug and drop about tablespoon, or two , of engine oil down into the cylinder, thru the spark plug hole. Put the compression gauge back on it, and do another compression check. If the compression comes up around 90-100psi, then you have ring problems. If it only goes up a little bit, then it's probably valve issues. It's going to go up a little bit in any case, because the oil will seal any rings a little better, and make the compression about 5-10psi higher. It's a bigger increase that you're looking for.
So, once you have that info, you can proceed.
Sometimes taking the head off can be difficult, and sometimes taking the barrel off can be difficult. But, other times it's easy. So, just have a go at removing the top end, if for nothing else than a de-coke, and have a look at all that is in there.
If you can't get something off, just ask.
DO NOT hammer or lever on any fins. Ask here for the accepted techniques to get these things off, if you have trouble. The fins will break off very easily, so don't whack on them.