If your gt40's are ported, and ported correctly. I would look at getting at least a gt40 intake and having Tmoss port the lower.
Tmoss ported my stock lower that I used on my gt40 heads before they were ported. I must say the opening of the intake was about a dead match to the unported heads and it was a great match IMHO.
When I got the heads ported I came across a explorer intake and Tmoss did a little port work to the lower. Again I think the match is great.
Depending on how your heads are ported I would look at a gt40 and if you can get one cheap enough have the lower ported. If you can not find a decent price on a gt40 and you really think the heads need something more than a stock gt40 intake can deliver...get something like a TFS or edlbrock intake. Really if you can not find a gt40 at a good price by the time you port it as well you could be looking at as much as aftermarket intakes. Explorer intakes are not hard to come buy and can be had for cheap so they are out there.