The original on our boat, (looks like the other photos posted) was made by Antal. It doesn’t match exactly traveler cars in the current catalog, but in our experience with other parts, Antal has some of these older things they made for OEM still in stock, if not actually in production. Contact the local distributor with dimensions and photos, including dimensions for the track.If you are not in Italy, it can take a while for the communications to go back and forth.
If the stainless steel loop is the part that broke, (most likely failure point) that can be replaced in place. No need to remove the car from the track. Do this if at all possible. While you have the car apart, it a good time to clean and inspect the sheaves.
I’d try very hard not to cut this track. Losing length would limit the utility of the traveler, and while it’s not much, every little thing adds up. On our boat, we have to lift the track to replace the outhaul car on the main boom. We found we did not have to remove the whole thing, it was surprisingly flexible
Pulling screws like this should be a routine maintenance thing, every few years. SOMEDAY it will need to be done, and it will never get any easier! Previous owners of our boat did this, and reinstalled them with a good lubricant. With the right tools we have never had any trouble getting them out.
The right tool starts with a proper sized bit. Older SMs used all slot drive screws, and exact size bits for these large screws can be hard to find, but are essential to do it right. The bit needs to have a blade the full width of the screw head, and be a good tight fit. I have these in 1/2 inch impact drive. If it is not a good fit, the head will mangle before full torque can be applied. Sometimes you can have better luck finding these in really large sizes by searching for “drag link sockets”
I start with a breaker bar, if that doesn’t turn, I’ll go with an extension. If you go to the extension, it can be a two person job. One holding the bit straight down in the screw, while the other applies the torque. You can use a 1/2” ratchet instead of the breaker bar, but you’ll risk damaging it with an extension. Steady, smooth torque—slowly increasing—is the best way to break them free and will minimize risk of breaking the bolt.
If hand torque doesn’t get me anywhere, I have resorted to using an impact wrench, but that does increase the chance of breaking something.
(headed to the Bahamas in a day or two...)