Difference between weber dcoe 31 and dcoe 18

[Spitbit]

Dear Sirs,
I'm planning to convert and old Triumph Spitfire 1500 with two weber carb.
The advised dcoe carbs for this application is dcoe 18.
In the bunch of pieces of my "workshop" i have two dcoe 31 that i have bought many year ago and restored.
From the research in internet i understand that dcoe 31 have a longer stroke and possibly different spring in the acceleration pump (i know that i can change) respect dcoe 18 and many other things that are replaceable.
I don't have found any info regarding the progression holes difference (position, diameter, number etc.) so ask you more info considering your big experience.
I don't want to ruin a good pair of original dcoe 31 by modifying the body or something like that you know...........

[rgh0]

The DCOE 31's should work fine for a 1500 spitfire with the right jetting and chokes. There should be no need to change anything else. There were a number of non functional differences in the castings and other parts between the 18's and 31's and the progression hole drillings were a little different I believe, but either would work on your car equally well.

cheers
Rohan