MY 86 560 does the same thing...I've replaced it so many times and it has melted sooo many times that when I'd turn it on you could even smell it burning in the cabin before it would blow. I did get the 30 amp blade fuse to replace it and just haven't relocated it YET because it hasn't blown since I replaced it. Believe it or not, while one fuse would blow, I would take the copper strip and insert it down into the melted hole to make a contact for the new fuse since it was nothing for it to connect to (on the bottom). Is this what you're doing. For some reason I know of 3 other people that have done the same thing.
I know that you'll have to relocate it and the relocation "kit" is only about $30 tops and you can do this yourself or have it done for under $100 (in atlanta anyway). Sorry, I don't have any illustrations myself but you'll have to remove the fuse box to run your wire to your new external fuse.
1970 250C SOLD
1971 250C SOLD