I have had this combination before but in a much bigger tank. I would suggest that if you are going to try this, to make sure and create a lot of hides/caves. Good luck to you and let us know how it works out.
They'll be fine until the convicts spawn / think of spawning. At which point, you'll find the jewels floating at the top missing scales.
A pair of convicts breeding in the 29 will quickly create space problems. I'm honestly not sure the Jewels will be able to deal with the + sized beatings even much smaller convicts will provide.
If you plan on having any breeding pairs, than, the 29 will be too small. If you just kept them singly. You may be ok. For best results I'd try to stick to females. I don't know how to sex Jewels but convicts are pretty easy. If it has orange on it's belly then it's female. Good luck.
ive kept these both in tanks plenty of times just with a higher PH but i did a 55 with 3 red jewels and 3 albino convicts
and its worked out very well, with a 29 i wouldnt try breeding though of either, niether can cross breed so just make sure
you watch for aggression if breeding happens on either side, cons and jewels can both be nasty and both breed a lot
i think they are an excellent match with the right sized tank. i have a pair of cons and a blood red jewel but in my 125. they scrap but they get a beating from my vieja x pair