Hi a10sausage and welcome to the forum and to what I imagine is a small band of A10 ers that have have grafted alloy heads on Flash engines.
To be honest I can't argue with those who advise against as my project is a bit of completion as yet, so as I have yet to ride it can't say how it will ride.
I already have a stock Gold Flash that is road going and is great fun to ride, so why am I converting my second one ?
1. because I can
2. because it's fun to do
3. If it's such a bad deal why did BSA make and sell so many Rockets ( would be interesting to know how many)
So far have rebiult both wheels with alloy rims and stainless spokes, powder coated the frame, tank, Painted the petrol tanh,oil tank and toolbox Wicked Red ( Citrion or Renualt pearlescent colour), new bushes and seals in G/Box, new bushes and bearings in engine plus rebore and new 9.5 pistons.
New carb ( may be asking forum members for advise re jetting ), alloy head with new valves and giudes, 357 camshaft, siamese exhaust, Goldie type headlight and indicators.
Forks rebushed, new stanchion, progressiive rate springs and double damped, hagon rear shocks.
SRM dynamo belt drive and cush drive nut, Lyford alloy clutch pressure plate and swapped six spring to four spring.
Sounds like a lot of work and expense but this is over a five year period, work constraints held me back but now I'm retired it should progress with more speed, I'm hoping to have it on the road this spring.
So I reckon if you want to have your Flash just a tad individualised - go for it you, keep the old parts you can always put it back to Flash status if you don't like it but you will have done it and won't always be wondering what if -----.
If you want to see how far I've got so far have a loook at "Rocket Gold Flash" in "bikes and pictures"
All the besst - Bill