It's interesting you should ask. I've personally used the Edelbrock Performer 289, the Ford Racing M-9424-A321 Cobra replica, an original C5OE iron 289 4 barrel intake, and am currently using an Edelbrock Performer RPM Air-Gap. I've used the Cobra replica, the Performer 289, and the Factory Iron intake on a set of stock 289 heads, and have used the Cobra replica and the stock iron 4bbl intake on a set of GT-40P heads, and have used the cobra replica and the RPM Air-Gap on my AFR 165s....so I actually have hands on experience, and I just so happen to also read alot of articles and books, crazy combination I know...
Comparing a stock 5.0 and a stock 289 isn't really the same thing. A stock 2bbl C Code 289 in good tune (but, again, bone stock) will only put out about 130hp at the rear wheels. Your 88 Crown Vic 5.0 had a higher lift roller cam and SEFI and made a lot more torque and 20-30 more hp than a stone stock 289 at the rear wheels. The 2bbl 289 has a hydraulic flat tappet that only has .380"-ish lift (if I remember right), and stock 289 heads don't flow as well as the later 5.0's E7TE heads, not to say that the E7TE flows a boat load of cfm, but on average they flow about 20cfm more per intake port than 289 heads, and that in conjunction with the higher lift 5.0 roller cam and the longer runners of the EFI manifold, make the EFI 5.0 a torquier, stronger motor.
The 5.0/302 and the early 289 are very, very similar as far as the block goes, but they are not the same thing. I guess the point I'm trying to make is, for a stone stock 289, with a cam that doesn't break .400" lift, with small port heads that only flow around 125cfm, with log style exhaust manifolds, etc, etc, that that motor will never see past 5000rpm. That being the case, a manifold like an Action Plus or a Performer which are rated to 5500rpm will be better suited for a stone stock single-point, low-compression 289 than a Performer RPM or equivalent.