And don't worry about buying Kadee parts you end up not using. In this hobby, there will always be another project, and those spare parts will come in handy.
Kadee parts will rarely, if ever, break.
I've replaced all the ancient horn-hook couplers from my teenage layout, mostly simple swaps from Athearn blue-box cars, but quite a few from old Mantua Talgo-equipped models, and even a number of modern models whose couplers just broke. Kadees have always been the upgrades, and I've never had one fail.
It takes an iron man to play with a toy iron horse.
Yep, a photo of the underside would help.
Rich
Alton Junction
As I said, " heavies" was the name used by Mantua. Model Power may have changed the name when they bought the Mantua RR line.
Some times you just have to take a shot. I removed one truck from the car. The truck and the coupler were actually two separate pieces with the coupler arm notched under the truck so they act like a one unit talgo. Once the coupler arm part was removed the truck can be put back and an assempled Kadee #5 can be glued to the car. Removing a bar that created a slot for the horn hook was necessary to allow the Kadee to fit. Couplers came out at the correct height and work fine. Actually, the box said Model Power Heavy Weight, not "Heavies". Thanks to all who replied.
"Heavies" were a line of freight cars produced by Mantua back around 1990. Model Power took over the Mantua/Tyco line around 2000, so your car is almost certainly a Mantua design built by Model Power. The only "heavies" I have bought were a stock car and a boxcar, both just used regular Kadee 5s. I guess I'd try that first and see if it works. Either a regular No. 5 Kadee or a whisker coupler.
Does this help?
https://www.kadee.com/hocc_model_power
"One difference between pessimists and optimists is that while pessimists are more often right, optimists have far more fun."
I advise that you have, or make, an accurate coupler height gauge before you start with anything more complicated than Kadee installation in a known-compatible box.
(example: Kadee 206)
The alignment and installation may be more complicated if you have 'Talgo-style' trucks (with the coupler boxes on extensions of the truck frame).
Can you post pictures, particularly of the undersides of the coupler mounts? See the first post on the forum for advice on posting pictures.
Some of the very old hornhook mounts are very narrow, or made of metal. It might be best to cut those off with a Dremel tool. You can get Kadee plastic draft gear boxes for mounting Kadee couplers, and either glue them in place after removing the horn hook boxes, or drill-and-tap for a screw mount if you prefer.
I had HO trains in the 1950s when I was a teenager. I've replaced a lot of hornhooks, and never failed in that task.
I have two Model Power "heavies" tank cars with, obviously, horn hook couplers. The couplers design and installation on the tank cars seems unique. Trying to figure out how to install Kadee's. Looking for a little advise before I remove the horn hooks.