First things first... the M62 engine is not commonly tuned in the UK. Neither in Germany or the USA however there are some bits that are available.
Intake - Get Air in - The Morgan implementation has quite a convoluted Air intake route over the Off-Side wheelarch. A Stage 1 enhancement would be to replace the standard air-box with an ITG cone filter. Alternatively Stage 2 (involves surgery) results in air bieng taken in via the front cowel (cutting a hole and using a cone air-filter directly onto the main throttle body). Stage 3 (involves major surgery) uses an S62 injector and throttle body set-up to draw air directly into the cylinderheads via holes in the top of the bonnet ala Tuscan Racer.
Exhaust - The current exhaust headers are a bit of a shocker... some after market manifolds and exhausts with side exits would sort that side of things out.
Cylinderheads - These can be flowed and there are gains to be had. You need an intake system though that can out-flow the proposed flow targets.
Enlarged Valves and solid lifters are also available from VAC Motorsports which would increase air flow and also max rpm... which is currently restricted by the use of hydraulic lifters.
Cams are readily available from VAC motorsports and these can be fitted with no other modifications... quite expensive for a few HP though.
http://www.vacmotorsports.com/Pistons, rods and crank are good for more power and should be balanced if you are going for a lot of revs... ie. much over stock.
VAC motorsports or TTV racing can make up a lightened flywheel which judging from my driving seems very heavy.
To make all this work you'll need an off board ECU probably from MBE or someone like that..
To hold all this back you'll need to upgrade the front brakes.. 6 pots are available from Mulfab or Richard Thorne.
Alternatively you can go for a stroker kit which is available from Noelle Motors in germany.. which punts you up to 5.2
http://www.noellemotors.de/5_2l_engine_basis_BMW_M62_B44.305+M554ce6bb0fb.0.htmlIf you were that way inclined personally I'd try to fit an S62.. which has most of the above and is available from Car Breakers from M5 V8's which is the same engine format see wikipedia M62, N62 S62 engine variants.
To do realistically any of the above.. budget about £20k...
So beyond Air Intake, Post Cat exhausts and re-map.. you're pretty much tuned up.