Here's the reply from areasix about the 500bhp.

Yes I am able to supply a 500HP unit no problem. The engine alone is £4950, and that's rocker box*to sump, and an assurance it will exceed 500HP on an engine dyno (much more on a Rolling Road).
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Be aware that you do need an appropriate Inlet manifold and turbo to achieve your goal. I will happily supply all parts inc ecu, injectors, loom, manifold, turbo wastegate, etc and you have the confidence that all parts will be reliable and appropriately specified.
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Diff between Silver and black-top - Silver has hydraulic followers, black top is mechanical. The basic port shape on black-top's is a little better on the inlet port. The black-top has a second idler after the exhaust cam to 'wrap' the belt better around the exh cam pulley. The main caps on a black-top are much shallower. Oil pump on silver-tops integrates the oil filter mounting. Water pump on Black-top sits forward of the block, silver top sits into block.
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Silver is easy to mount into older chassis, black-top fit's easier into later models 2001 onwards, but can fit into earlies with custom mounts.


Also was thinking about putting the cosworth engine in. Is that too much work?