An IJ or more northerly coastal carpet python would do well kept similarly to GTPs, though I wouldn't exactly say it's a two way street for the GTPs. I wouldn't house a 20lb+ carpet with a 5lb GTP however, so IJs might be a better choice.
I don't like to cohabitate snakes. Even though I've never seen it in morelia, many snakes you might not think about (even ball pythons) have been witnessed being cannibals.
In addition, cohabitation can result in male-on-male combat, or unintended clutches. This may not be an issue for you in particular, since it sounds like you're intending to shoot for carpondros.
As far as how carpondros are made, everyone I know who has had successful clutches, or even just successful locks, houses snakes seperately and then introduces them during the breeding season. Sometimes they are housed together for weeks on end, though many people do a couple days at a time, and give the snakes some rest time. There are enough cases of males "over-breeding" themselves to death that I like to give my males time off. I'm far from an expert on the "how-tos" of hybridization with snakes, but for many people, trickery is needed to induce a lock. Scenting the cage with the shed (sprayed with a bit of water) of a female that is the same species as the male you're trying to hybridize with is a popular technique. Another is smearing sperm plugs of another male (same species as your breeder male) across the females back.
Hybridization of snakes itself is super tricky. Your likelihood of getting a clutch of unfertilized slugs is through the roof. I don't know the exact statistics of successful F1 carpondro clutches, but I'd guess that only around 25% of clutches laid have at least one viable egg.. and the chances of a clutch being laid is significantly less than if you're not shooting for a hybrid.
Back to cohabitation, females also can suffer if bred successively year after year, season after season, without one or two seasons off. This can be an issue if you house the same two snakes together for years and years.
There are enough issues with co-habitation. It is certainly do-able, but I don't recommend it just for someone who wants to save on space. Have a backup cage for one of the animals if you're intending on housing a pair together, just in case it doesn't work out, or you want to give the female a year to herself.
