If you're going to try Goldie cams the ones to try are either Touring cams...part nos. 65-2448 (in) and 65-2450 (ex) or Scrambles cams 65-2446 (in & ex)....
The touring cams are a straight fit..
The Scrambles cams will also fit straight in. However, I haven't personally fitted the scrambles cams to a sidevalve and am unsure of the benefits, if any, of increasing the cam performance that much without doing anything else to help take advantage of the upgrade....It should be considered that extreme cam improvements in isolation will not necessarily lead to much of a power increase and can actually cause problems...they are just one part of a more complete package of alterations designed to improve cylinder filling (volumetric efficiency)...
Additional things to check with the higher lift of the scrambles cams are that the valve springs don't become 'coilbound', that the valve spring collars don't contact the valve guides, that you can still set the valve lifter correctly (the base circle diameter of scrambles cams is less than standard ones so the follower will drop further) and that you have sufficient clearance above the valve heads....
It is possible someone else from the forum has tried the scrambles cams and will be able to answer some of the points I've detailed above..
With touring cams I fit an inner valve spring as well as the standard spring....I use BSA C15 inners and I know some use the inners from an Ariel single as a suitable alternative....Inner springs will be even more necessary with scrambles cams fitted...
In terms of a 'package' of improvements to make a BSA single go quickly the first, and key, thing to do is lighten the crankshaft..Below is a picture of the crank for my M20 sprinter...This would be too radical for a side valve road engine (unless you have a serious mental problem!) but a decent weight reduction here would be a first step, followed by porting and cam improvements etc....Ian
Bryce lad, to get full benefits of goldie cams you need more compression, better gas flowing etc.
my 55 m20 has scramble cams but ground to a different profile to suit side valves, also welded up head, gas flowed, larger 389 carb , A10 inner valve springs, valve clearance set at 16thou (to get compression as valves are open nearly all the time!)power is about the same as my 500 red hunter 80+ top speed with acceleration to match. Unless your bottom end is in top condition don't even bother!
Hi Adrian...It's an American Carillo rod in the standard length....You can't really shorten the rod on a sidevalve because of the height required in the barrel to house the valves and ports...
I don't want to quote the exact crank weight here on an open forum...Suffice to say if I was doing a fast M20 for the road I'd remove at least 3 to 4 lbs...Ian 
Hi Adrian...If you need more detailed information for a project mail me off forum...Ian
One further point before engaging in extensive lightening of either M20 or M21 flywheels, check that you have the steel flywheels and not the cast iron ones...Ian
Hi Adrian..All the wartime and postwar OHV engines had steel flywheels (B29/B30/B31/B33/M33)..The M20 and M21 had different materials at different times, sometimes determined by cost (cast wheels are much cheaper to produce) and sometimes by the demands of the user..(AA, War Department etc.)
Cast iron M20 flywheels are less common than the steel ones I have found...and the reverse is the case with the M21...at least that's how it is in the UK...
As a general rule flywheels marked with a part number where the second set of numbers begin with a '6'..66-635 for example, are steel...those with a '7' for the first digit..66-754 for example...are cast iron.
Sometimes you will find flywheels which don't conform to this numbering pattern and have a 'random' number...These are generally cast iron in my experience...
See above for my e mail address....Ian
email (option): ian@wright52.plus.com
Or below... ...Ian
email (option): ian@wright52.plus.com