Welcome to the Herd, Swimmingrod!
If you want to build the
Monogram P-61 (not Revell, regardless of the logo on the box), then look for an old boxing, as others have suggested. The "white box" boxing was the first, back in the mid-70s. The box was overall white, with a photo of the built model on the lid. It included Shep Paine's "Tips on Building Dioramas" brochure, featuring the diorama Shep built with the Black Widow (see the brochure
here).
Black Sheep mentioned this: over the years, and through subsequent releases, and merger with Revell, the molds have worn. More recent releases are more likely to have fit issues, flash, etc.
It's not a bad kit, but I would buy the older release off the secondary market, eg, eBay, at shows, at club meetings, than the latest release.
That goes for pretty much any kit released by Monogram, too. I build Monogram, and Revell, which were the brands I built as a kid (I was born in 1964). But I buy older boxings on the second-hand market. I don't care if the kit includes the decals, either, and I have gotten away without instructions. Bagged kits are fine; as long as all the parts are there, I'm happy. But the older boxings were popped when the molds were still relatively new.
To return to your original question about a 737 kit, I'm afraid I can't really help, because I don't build airliners, or jets, really. I haven't built an airliner since I was a kid, an Aurora Boeing 727. I couldn't even say, off the top of my head, who today makes airliners, but I do know that there are kits on the market.
Someone else mentioned
Scalemates, which is a scale modeling database in wiki form. It's very useful, a lot of good info there, though it's all member-driven. That is, what's there is there because someone added the info. So you might not find something, but there is a ton of info there. I'd visit Scalemates and search on "boeing 737" as a start. From there, you could search online for vendors who carry any kit you find.
Hope that helps!
Best regards,
Brad