200R4 update
I ended up calling Wilcap then a couple months ago and he said he's made a few slant 6 to 200r4 adapter plates but there isn't a very high demand for them. He said he might make a few just to have on hand cause another guy had emailed him about on the same day I called him. If I remember right he said the price would be around $600-650, can't remember if that includes the modified mini starter or not.