Pulling info from Table depending on size

Dear Forum
I wondering if someone can help me configure a formula.
I have a data entered in A1:I8 that contains the data I will want to pull info from.
The Size of Valve are in cells A1:H1.
The intent is for the user to enter a size of container in cell L1 and enter a BD dimension in L2. I then want the answer to populate cell L3.
Right now I have a VLookup formula in cell L3, which would work if the only valve size is 8". However I want it such that if the user changed the Size of Valve (cell L1) to another value that it would adjust 'lookup' to correspond to the actual user's entry.
I have a feeling an INDEX formula would be required, but I'm not very familar with constructing them from scratch.

Any help would be appreciated.

Try this formula in L3 (but first, replace the values in A1:H1 with numerics only - get rid of the " (inch) symbols OR add the inch symbols to your drop down list values for L1)

=VLOOKUP(L2,INDEX(A2:H2,,MATCH(L1,A1:H1,0)):I8,10-MATCH(L1,A1:H1,0),1)