Dimensions

[racehead-1]

I have this cylinder head that is fron a Citroen four cylinder 1100cc. The intake valve are 37 mm and the exhaust 27mm.
The exhaust valve should be 70% of the intake, by doing the math it turns out that the exhaust valve need to be 31mm.
So there is the need for a new seat and valve. My idea before doing this I wanted to keep the same valve and in the throat increase the area. The exhaust seat is 3.5mm and would be reduced to 1.5mm. The bowl would be opened up on the intake to 80% and on the exhaust 72%.It is a big problen in getting oversize valve for this engine. Does anybody can recomend a place for the valve and seats?