Don't discount the adjustable valves for your armstrongs. A much cheaper and easier conversion. Whip the armstrongs out, flush, clean, swap valves, fill, bleed and fit.

"Y mae dafad ddu ym mhob praidd"
1972 4/4, 1981 MGBGT, 1984 FLHT1340, 1980 XLH1000, 1990 ZX10