One thing you do not want to do is remove the plastic runners from the UIM completely. This has been tried by a few GPGTers at the track with negative results.
ZZP'* HVII (http://www.easyperformance.com/
article in tech info) replaces the runners in the UIM with a smoothed bellmouthed transition.
This jump down in take runner length has been found to be way too sort to see 1/4 mile gains on a realtively stock car. (no cam or rockers)
They don't produce this anymore though so you would need to find a second hand piece.
The plastic intake runners could be cut a few different ways to shorten the runner length. The hard part would be keeping everything together in there since they are joined at the top.
And theres always swapping over an F-body upper/lower intake combo for the shorter runner length. Thats is lot of work and I have yet to see any gains from it.