looks like good fun mate! think I've got toomuch mechanical sympathy to do that, sprinted a mk1 last year and struggled to get the back out much on road tyres!
in regards to the bucket seat, I use a CG lock sold by demon tweeks I think, which braces you in really well and fits to the original seat belt, but is only £30-40 as opposed to buying a bucket seat and harness.
Cheers
Dan