My dad ran those in the '71 Westfalia I grew up with. Those, along with an Engle 110 and some small single barrel carbs made the thing move really well, he even got a speeding ticket in Texas on family vacation for going 80 something! Cop supposedly was stunned that a bus could go that fast! It was great until it got warm, distored the cylinders, and blew oil by the rings!
I think he said he put in two or three sets of those slip ins over the years. In a bus, bad idea. If it's a motor that's well thought out and cools itself very well then I think you'll be fine. Thicker cylinder walls just give you more insurance if you do get it warm, keep the head temps down and you'll be fine. I've got a forged set that I'll be trying out in the GTV, soon I hope!