just starting off on first build!!! can the rear design of the avon sierra axle be grafted to the rest of the locost "book" chassis also on the locost are the seats mounted to the floor? or extra rails added regards martin

Yes the Avon design for IRS can easily be grafted onto the back of a Book chassis. The rear bulkheads are inclined at different angles so just decide which one you are going to use and make allowances to keep the IRS in the same relevant position.
If you plan to use the Avon design for rear uprights and wishbones be aware that the rear wishbones converge and therefore produce undesireable camber angles. Moving the wishbone pick up points or altering the upright design to correct this is also easy if tackled early enough in the build.
My advice would be to build the book chassis up to and including the rear bulkhead, mount the diff on the bulkhead and base your IRS loosly on the Avon.
As for the seats, mine (roadster sevens) will be mounted directly onto extra rails added to the chassis.

Enjoy your build

Mick

Yep, it can be, though wether it's much of an upgrade from the live axle is open to debate. Personaly I thought it was such a poor design* I chopped it back off my chassis and went for a De-dion axle instead.

*Minimal triangulation, poor geometry and no adjustability for toe which was the main decider for me. Without adjustable toe, you will have to weld the brackets onto your chassis with sub-mm accuracy to get the correct toe and have it the same either side.

Thanx for the valued input i dont really hav e a preference, just local scrap yards full of sierras even been offered a chevette saloon for a tenner seems possible donor for axle fuel tank etc. shame about the engine i collect steel next week,so hear goes i intend to build slowly as my 8 year old is the forman

Oh dear, im doing the same thing and have put the framework in already for the avon rear end and am now wondering if i should have done. Just out of interest what DeDion rear are people using? is it the GTS one? If so how are people finding availability of GTS kit?

I'm using the GTS one, although I don't actually have it yet. I agonised for ages over using IRS as I bought the chassis part built with the Avon rear end already in place, but decided that redesiging it to my satisfaction was just going to take too long.

In fairness it probably does the job OK if assembled accurately (some kind of jig to hold the hubs at a set angle whilst tacking the suspension brackets is probably a good idea).

Martin I'm using rod ends on the outside of both top and bottom w/bones to allow the upright to be adjusted for camber and toe and normal bushes on the inside, also the top inner w/bone brackets have three sets of holes, the top hole is as per the book the other two are just in case.
Wimmera