Yep,install the H.O cam and Explorer intake,Mustang Exhaust and go.It already has roller lifters in it.The E-6 heads as well.They aren't much good,but a set of E-7's from an EFI 5.0 truck will fix that.I had an E303,ported E-7 heads and a lot of fun with my last engine.Never any issues (with the flat top pistons).But,the H.O cam will do just fine without any worries.
Panther body cars (Crown Vic, Grand Marquis, Town Car) used 16-pound injectors, same as the Fox T-bird/Cougar/lo-po 5.0 Mark VII cars. The HO cam, E7 heads, and Fox 5.0 ECM make 19-pound injectors mandatory. The intake manifolds are also slightly different, and the lo-po 5.0's used a smaller-bore throttle body and EGR spacer. The intake is slightly different between the non-HO and HO motors, too - not just the fact that they point opposite directions (they're both reversible, actually), but that they have slightly different flow rates. (Can't remember right off hand if it's the upper or lower manifold, specifically, that's different between the two...
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As far as the block itself goes, all '86+ EFI Panther cars had roller 5.0's, so no need for any conversion to be done there. Aside from the piston-to-valve clearance issues, E7 heads are a direct bolt-on.
Also, just an FYI, the firing order on the lo-po 5.0's is different than on the HO motors.
I'd bet you could use the GT40 heads as long as you stick with the H.O cam.
The issue of flat-top pistons and E7 heads seems to be hit-and-miss from what I've read; some folks have been able to just slap on a set of E7's with an HO cam and have no problems, while others have checked their piston-to-valve clearance before assembly and found that it's a no-go deal without either notching the pistons or switching to pistons cast with valve reliefs. You could try it and see how it clears before you fully assemble it, but I'd say the odds aren't in your favor of getting E7's on there without notching the pistons, even with an HO cam.
