Thanks @Winblows. I look forward to the comparison. Fingers crossed the OLD top plate makes no difference to performance as the 1904 plate (pictured above) makes that head look a little tamer - like grinding down the tip of a tiger's teeth. The only thing I want changed on my Fatip is the handle.Yes, the top plate from a Gillette old type OC.
I don't have the tool to measure the blade gap, but I think this operation makes the result-Frankenrazor a bit milder than the original Fatip.
I'll soon make an outright test of the two heads, then I'll make a picture of these two at a more close distance.
Here is a picture of a Fatip base plate with a Merkur 1904 top plate (very similar to the Gillette).