The 5L M119 greatly improves with ported/portmatched heads+intake runners+exhaust manifolds and more aggressive cams. This will confirm you every tuner that tuned the M119 back then. The stock cams are relatively mild, especially the later ones. While the heads already flow "good"
(well its a 4 Valve so it has to be) there is still room for improvement. If there would be none or just 5HP, no tuner would have offered it. Remember one of the Tuner with the best references for M119, M120, M113, etc was Hagmann. The Hagmann owner himself told me, his cam profile (10.4 Lift intake and 10.4 exhaust, 264°intake/252°exhaust) with the stock heads and after LH Adjustment will produce around 355HP. When you Portmatch and Port the Heads it will be 370HP
(dyno verified!), Max HP shifts to 6000RPM. Thats 15HP/NM that the Portmatch Porting alone will give, dont forget that Porting/Portmatch will often greatly improve throttle responsiveness and overall "feel" of the engine when it revs up. You can read this result at basically every Porting/Portmatch experience of a user
(brand/car independent).
Bernard will offer in the future a tuning between the 5L and the 6L with a 5.6L
(or was it a 5.4L?) engine with just different pistons
(because of IIRC compression and displacement), his Stage 2 or Stage 3 Ported CNC Heads, Agressive Cams, ported stock exhaust headers and it will Rev to 7000RPM!, redline at 7200RPM, 11:1 compression, LH-Jetronic.
This engine will Produce 400HP (DIN) and Torque inbetween the 5L and 6L, but of course not the massive 6.xL Torques. Different high-revving engine characteristic, i dont know if he already had a succesfull prototype of this engine so far
(he was pretty silent about it), but i believe him with his Power advertisements, as they are always very conservative.
Bernard offers CNC Ported M119 heads that massively englarged the intake ports, shorter and oval-tip shaped valveguides, Multi-angle valve-seat cut, maximized exhaust ports and Portmatched Intake Runners+Exhaust manifolds
(both are also greatly enlarged to portmatch the enlarged intake and exhaust ports in the heads). He already sold a couple of sets of these Heads. The price is including 19% VAT IIRC 3900€ for both, you basically have brand new heads then that are tuned to the maximum. Some of the customers were people with 6L Brabus or 6L AMG 500Es, they noticed an improvement in reaction to throttle inputs, they told him and he told me that the cars equipped with his heads got more "agressive" and gain especially near top till readline. I share you one pic of an Intake runner of his CNC machined heads. The funny thing is... if you look at stock 6L AMG heads or the 6L Brabus heads, you notice these heads are already ported/portmatched and the surface is very smooth. Brabus also shortened the valve-guides on their M119 and M120 head rework on top of that. And still Bernard claims his CNC heads flow 15% !!! better than the Ported/Portmatched AMG heads.
Pictures of his Stage1 CNC heads. Notice especially the big exhuast Ports. I can tell you from my own experience that they are stock only approx 60-70% of that opening!:




These are Brabus Ported Intake runners (sorry not more pictures taken):

These are the E50AMG Exhaust Manifolds. Bernard says these engines are artificially throttled, they are stronger if exhaust opened up.
Yes Dave i also thing they have no WOT-enrichment. I think i secure one of these engines, a friend of mine selling one currently. Might be good if optimized for a 500E.:

Regarding your Question Roger,
i think Brabus machined the Valvespring/Tappet Bore deeper for safety margins. The Hydraulic lifters/tappets were 2mm longer/deeper back in the days. The current ones are 2mm shorter. And maybe because of their used Valvesprings. All i can tell you is that it works with a stock Valvespring Bore with the 10.4mm Lift. IF it will work with 11mm, you need to put the Valveguides down further into the ports and you need good springs that can compress so much but still are strong enough.