I have 3 point lap and shoulder belts in my Bugeye. These are the ones that VB sells
3 point lap/shoulder seat belt in the right column and center of the catalog page I have linked to.
I have a rollbar and simply removed one of its bolts to install the hardware for the shoulder anchor bracket. Sorry I don't have a photo, but it is located near the top of the rear fender well.
The secret to making these belts functional is getting them adjusted right. What you want is for the buckle to be low on your waist, down near the transmission tunnel. If the buckle isn't "low and tight across your waist" then the belt going to your shoulder is going keep slipping off.
It is a real pain to get these particular belts adjusted so they fit though, I must say, especially when a person who isn't ordinarily riding around with you becomes a passenger. And, the belts have a tendency to twist and get in the way, and the buckle is forever falling into the gap between the seat and the tunnel.
Retractable belts would be much easier to use for these reasons. I hesitated to buy the generic ones because I was not sure that I could get the geometry right. There is no way to adjust the distance between the floor and buckle on the ones that VB offers (upper left hand corner of that page).
Another option I might consider for the future is drilling the rollbar and bolting the hardware that anchors the shoulder belt so that it is above the shoulder, similar to what you have in a modern automobile. I haven't driven around enough with them installed to decide whether that is necessary.
The main thing, as I noted above, is to take your time before you leave and adjust the belts so they fit right. And, of course, ALWAYS drive very carefully.
Good luck!
CL