Anybody know of a driveshaft safety loop that will be ok with a 4" driveshaft?

What loop? I'm assuming you mean the Lakewood one. My 3" shaft fits fine through the loop however the 1350 series u-joint yokes wouldn't fit through until I modified the loop a bit.

I have a universal loop on my truck with a huge 4" shaft. There's about 1/16" clearance on each side of the shaft. The shaft doesn't move side to side so it never touches.

Where are you getting a 4" shaft from?

Might have a deal on one from a guy that works at Dana. It's the chromemoly 4" NASCAR style ones. Not my first choice, but for the price..

And I meant any loop. I'm just looking for something that'll work. I have a Spohn ds loop now and it's 5". So I won't have to worry about the 4" shaft ever touching the loop?

jegs makes a universal one, but it isn't very universal. if i were you i'd just make one to pass NHRA rules.

What are your recomendations as far as a 4inch shaft compared to a 3inch shaft? Has anyone ever used a 4inch shaft?

I have the Lakewood DS loop and noticed that with my stock driveshaft, the loop is pretty close to the driveshaft. I'm planning on modifying the bottom portion of the loop to allow for a larger diameter shaft. This will cut into the space which is normally taken up by the torque arm, but I have a SSM rear suspension, so that's not an issue for me. Here is a picture of my template next to the Lakewood piece:

The paper cutout would be the outline of the new piece.