The pinto water pump inlet and thermostat out are oval!! they seem to vary by about 2mm

Waterpump - 38/40mm
thermo - 30/32mm

how exact do i have to be with silicon hose? Is it very stretchy?

OVAL i tells ya!!

silicon will do an oval easypeasy. just take an average of the diameters for the size. you can push it onto pipe a couple of mm bigger no probs.

like a glove!

Thanks!!