In the build.prop file there is a "fingerprint".
Stock 351 has this fingerprint:
while SimpleStreak has this fingerprint:
The Android Market uses this fingerprint to identify your phone and based on the phone you are using some apps may not show up. Depending on the ROM you using previously the Market might be seeing your phone differently and the apps that show up may be different.
There are other ways that the market identifies your phone, but sometimes editing the fingerprint in build.prop is all you have to do to see apps you had prior to installing a custom ROM.
Never ask before searching!
Current Device: AT&T LG Optimus G, stock, rooted JB
Retired Devices: At&T Galaxy Skyrocket, Dell Venue, Dell Streak, Moto Flipside, Moto Backflip, Samsung Eternity