the 6.5-20 LR is 2" longer than the 4.5-14 model.
Remember, their objective diameter is the same.
Your only problem would be if you are either:
A) using a tapered scope base, in which case you should measure how much clearance you have with the 4.5-14 and then apply 2" additional length at the degree of taper (which is probably one third of a degree, which ain't much friend)
or B) if your barrel diameter/taper gets bigger after the junction with your action, and that seems a bit unlikely (a "bit" meaning like my chances of winning all lotteries in all states at the same time).
If you plan on using lens covers, be sure to take them into account.
[ 11-01-2003: Message edited by: Nate Haler ]