I designed parts that help to upgrade all WPL trucks and that parts can be found here:
https://www.thingiverse.com/Adrian202/designs
If You want to sell it just ask me, I know people print it and sell it to friends but if Someone want to sell it like here:
https://www.ebay.co.uk/itm/112824235258?ul_noapp=true
Just ask because I can post links in My movies and people ask me if I can print that but My printer is still dead

Also parts to modify and some beta design are posted here:
https://www.tinkercad.com/users/ijdXrBIYp5t-adrian202gt
But leafsprings are still not tested and can't work on current computer so that design still wait

If You got any questions You can ask here or just on Facebook:
https://web.facebook.com/Adrian202RC