It would take halve a brain SFA to DIY your won EFI inlet manifold these days
will all the bits available online.
Roland Twin weber manifold with cheap brass injection inserts (heaps of patterns)
250-300 aud all up
https://www.google.co.jp/search?q=bras ... _AUIEigC&biw=1326&bih=658
https://poojametal.com/brass-inserts-for-mouldings/Xcessive manufacturing plenum 225usd
https://xcessivemanufacturing.com/niss ... ms-flanges-ui-efp-n1.html
or even cheaper 20 bucks from centre road wreckers and diy cut up a Hyundai v6 inlet
use Permatex 84209 PermaPoxy 4 Minute Multi-Metal Epoxy to bond it all
and self tap inserts for extra strength onto flat piece of alloy plate
to act as a flange to sit between them you can port flange to taper
into manifold inlets and Bobs your Aunty.
cheap and easy for any halve wit prob less than 700aud and will look awesome
As for exhaust manifold better pay someone to do one and if you do an inlet
design as mentioned above, then you can pay even for a billet unit with leftover
change from what some of these advertised custom ones are priced at.