Ziggy,
The older I get the more confused I am! And the timeline is only in my head.
I am most aware of ther 96-99 years as I bought a Heckler in 1997. I have scanned sections of my 1997 catalogue earlier and posted them here:
http://www.retrobike.co.uk/forum/viewtopic.php?t=54519
Now in this 1997 catalogue even with the double crown forks there's no disc tabs so I think that makes my own frame with tabs a '98 "model".
Note also no brace plates for the main pivot welded between the seat dand down tube just above the BB shell. IIRC earlier Hecklers did have the braces, also a feature of the Tazmon design that preceeds the Heckler, but the Tazmon has no braces in 1997 either.
The '96-'977 Medium frame featured a straight top tube when I tested it, but the Large in the catalogue has a bent top tube. The design gives good standover clearance and allows positioning of the top tube damper mount so as not to upset the shock rates between sizes. The blurb also mentions the Heckler SL (for Super Light) essentially the same geometry but with thinner gauge, butted and machined tubes to shed weight. The first SL's came with a 200 lbs rider weight limit and were ball burnished alloy to save weight on paint.
Later editions lost even more weight whilst simultaneously relaxing the rider weight limit, and the SL became a big seller. Eventually the plain Heckler was dropped and the SL became the "Superlight" line. And that bent top tube has become a trademark of the Heckler and Superlight and is also is very prominent in the current crop of Santa Cruz designs.
I am still puzzled by the small frame with the bent top tube. It sort of contradicts the positioning of the damper mount argument too. I think indeed it could be a feature of the later models but that is not consistent with the lack of disc tabs. And details that I know have variations like the seatstay brace and the downtube decals are identical to my 97-98 again.
Enjoy!!