Cortina-student

Hello everyone! I have Xflow with Hepolite .030" pistons, bcf2 cam, larger valves (any larger cannot fit), double valvesprings etc. I did clay test to prove valve to piston clearance and it was only maybe 1.2 mm. How tight it is actually, if i will drive mostly under 7000 rpm (bcf2 range is 2500-6500rpm)? Is it good idea to put all things together with only around 1.2mm valve to piston clearance? Sorry my english, no Google translator. Greetings from Finland