I did something like this for our old CoD2 server. I replaced the smoke grenade model with that teddy bear model that's built into the game, and made it explode like a satchel charge.
The trick is finding xmodels that hide the player's hand model. The american grenade (the time bomb) that you came up with, though, looks pretty good ... like the hand is actually holding the bomb.
You can also change the explosion type in the weapon file to something else like a rocket, i.e. "projExplosionType\rocket\" in the grenade's weapon file, which will make for a bigger blast. You can also change the "projExplosionEffect" setting to use any of the explosion effects you'll find it in the fx/explosions folder in pakuo00, and you can combine certain types of effects just by cutting and pasting two into the same .efx file and putting that new file in the fx folder of your mod. Sometimes it will work, sometimes it won't. It's a lot of fun, though, to experiment with the different stock .efx files to see what kind of hellacious blasts you can make.
Anyway, modding is really what keeps the game interesting after all these years. Keep it up.
