Welcome. Great mods, Hoki. Those are very good options. The reason it won't rev is likely to be the stock 256 degree cam.
The rev range of the 4.1 is limited by its stock camshaft profile and that is there bacause of the poor strength of the valve gear. It has small intake ports, and one of the best cylinder heads for low end torque that money can buy.
It is limited by the weight of the pushrods and valve gear, and the tendancy for certain parts to pull out under load. Like the rocker studs which bolt the rockers to the head.
First step, do this>
Dismantle valve springs and seals using the compressed air process following full saftey precoations. See if the yellow valve springs test up to the minimum requirements for seat and wide open nose pressure. Take them to a mechanic. See what the rise of the lifter is in the block with a dial gauge when the cam is moved from zero to full lift. If its over 6.5 mms on the dial, then its got a higher lift cam already. But it won't .It'll be a stock 6.3 mm lift item fo sure. Someones just put killer valve spings on it which are more than likely too stiff for the stock cam. The idea is to use just enough spring tension to stop valve float and lifter pump up.
There are two options with the cam. The stock Crow grinds allow an XF 4.1 EFI style 264 degree cam profile to be made, which allows all the stock valve gear to be used. These have the eccentric on them which allow a fuel pump to be driven, the 4.1 XF EFI doesn't have one. That is fine for 165 net flywheel hp without headers, just like the stock XF EFI.
Next step up is to fit a 280 degree cam with about 470 to 490 thou lift, with about 215 degrees duration at 50 thou lift. Well over 195 net flywheel ponies with that cam wih nothing but a good carb and exhast. There is plenty of power hiding in there.
Crow cams or Kelfords can sort the right kind of cam out. Do yourself a favour and get either new or reground lifters, new cam with the right cam 525 thou distributor drive, check the pushrods, get new rocker balls (called Sled Fulcrums), buy the common and good good Isky big Block Chev retainers (same parts as the 351c, 429's and 454's ran), get the good valves, rework the keepers by shaving each of the 24 collets 40 thou so the multi grove valves are locked solid and don't allow the valve to spin. Then go for a new replacement timing chain and drive set.
Set asside some beer money for a Permaset head gasket, 14 new Cleveland head studs, and a light shave of the head will be all you need to look at if the block and pistons are fine.
The 4.1 won't ever rev to 6000 rpm like an AU or BA 4.0 will unless you fit longer rods, and Phase 3 Falcon valve gear. Stock rod bolts are like plastercine, and need to be biffed and replaced to go over 5000 rpm. A stocker will handle 4800 rpm repeatedly.
The real saving on these engines is the reduced cost of ownership on a OHC engine. No EFI or ignition hassles, no problems matching aftermarket cams to 1.8:1 or 2.0:1 rockers, or the expense of the trick conical springs. No issues with head cracks or substandard head bolts . It's impossible to kill the Honda alloy head casting, the XE engine has nicer heads and doesn't have a heap of ignition advance. The rest of the engine can hack a heap of punishment.
Due to piston ring changes, high swirl heads, and an aggressive spark advance curve, the XF's were detonation prone and 4.1's wouldn't go over 4500 rpm, so stick with your engine.
. Does this mean the manifold and carby wont make any difference without the bigger cam.