I have a trig on the flamingo , same as the tregg (brothers I believe) but the c piece is cast & extends out further , I use 2 pieces of 1/2" retic pipe , one in the poly block & one in the c piece leave the rear door open & can line it up easy , the missus is happy too as she can use the pipe to align the poly block and keep her fingers clear , you need to heat the pipe & pull apart to reduce the dia , then cut in half
Ta Keith