for those who were kind enough to respond on the forum and via pm, and for anyone else who might search and find this thread in the future - here's what happened ....
insurers accepted it was a valid claim and covered by my policy. I sent them plenty of photo's and a components list for each bike (down to the make and model of cable wire!). They outsourced it to a claims handler company who contacted me to say that they would work with their suppliers to find "new for old" "like for like" replacements for both bikes.
The single speed on-one inbred was relatively easy. Their supplier couldn't offer me an on-one (only on-one sell them) so they offered me a range of other steel single speed specific frames with the same components or same standard of components (at least) as was on my home assembled inbred. I had to challenge a number of their proposed components as not "like for like" but after a few weeks of haggling they are now doing me a custom build based on a Genesis Fortitude 29er SS frame with Halo wheels, race face crank, nobby nics and easton a50 finishing kit. Bonkers as my inbred was a second hand frame with bitsnbobs assembled from online clearances, second hand bargains and bits I had lying around the parts box. this replacement must be worth about 3 times what the inbred cost to assemble - BUT I was 100% honest throughout and this is what I'm getting. Happy days!!!
as for the 91 Kona Cindercone, again they worked hard to please me with a new custom build and the offers were extremely impressive (Salsa Vaya Travel, SLX gears, Xt brakes) but ultimately they could only offer touring frames with v-brake mounts. What I wanted from this one was some cash so that i could get my hands on another retro kona. I didn't ask for money but I continued to decline their proposed replacements, for very valid reasons, until they concluded that a cash settlement would be more appropriate. They calculate it by offering what their proposed replacement would have cost them to assemble. They get a hefty discount from their supplier, but even so the sum offered was £944. I accepted and bought a beautiful 95 cindercone frame from here which I am in the process of assembling.
Be assertive. insist that "like for like" means just that, and if their supplier can't deliver it, then they need to offer a "new for old" value cash settlement.