I am seeking the I.D. of vacuum tubing for 1974 HILUX 18 R-C engine. Thank you.

 

Most Toyota vacuum hoses are 1/8" inside diameter. 1974 is early so it may be different. Best thing is to try a piece and see how it fits, or use a caliper to get an exact size.
Go with silicone if you can find it. Holds up much better than standard rubber.

 

Thank you. Good advice on use of silicone.