What a lovely kit! Tamiya at its best: Parts are very detailed but not excessively fragile, and fit is perfect even for very detailed items, such as the chassis strut that joins the firewall to the right front suspension mounting, passing below the intake manifold and through the exhaust manifold. (This is not visible in the picture below as the motor needs to go in first). Parts are well formed with minimal sinkholes or part lines, and the connection from the part to the sprue is often through a mounting point, which you will normally be filing smooth anyway, rather than a visible area of the part where you'll have to touch it up once you cut it off the sprue.
The Gullwing doors, of course, were dictated by the wide sills, which were in turn dictated by the classic three-dimensional space frame made up of lots of little tubes. At its most complex, this type of chassis design led to extremes like the Maserati Birdcages from the late '50s and early '60s. At its simplest, it offered an entire generation of British back-yard builders, like Lotus, TVR or Ginetta. the opportunity to build a decent chassis in reasonable quantities using 4130 chrome-moly tubing and a home welding setup. The Tamiya kit provides a very detailed replica of the chassis and it will be a shame to hide this under the body work.
I spent about 18 months working for the local Mercedes-Benz dealership as an apprentice mechanic back in the mid-70s and recall these lovely cars still turning up occasionally, including a blue-grey roadster belonging to one P.E. Trudeau. The stock hubcaps, painted to match the body, were very classy and understated, but I ordered the Rudge wheels, made by Historic Racing Miniatures, from Strada Sports. Painted black, these will provide a nice contrast to a classic silver body. An alternative is to paint the body a non-standard black; there is a very nice picture online of a 300SL roadster, in black with black Rudge wheels, that is very striking. Decisions, decisions. Either way the dark red interior will be a nice contrast.
The 300 SL was a study in contrasts. The engine is an overhead cam straight 6 with fuel injection and an aluminum head; on the other hand the Tamiya model implies the exhaust ports in the middle cylinders (2 and 3; 4 and 5) are siamesed, something I don't recall from the 300 sedans of the same period. Rear suspension is by swing-arms, and does not incorporate all the camber compensation bits that appeared on the subsequent 230/250/280 SL, as well as the mighty and legendary 6.3. Brakes are drums all around. So a mix of state of the art for the late '50s, and some legacy bits that really should have been ditched a lot sooner. My time as an apprentice corresponded with the introduction of the 450 SL and SE/SEL, the first with fully independent rear suspension, and the 280 sedan, with IRS and a proper twin-cam six; MB at the time was never one to leap out in front of a 'fad'.
In any case, this is a superb kit, and while very rewarding for a skilled builder, will probably not be as tricky as the Revell BRE 510 for a beginner.