ugh.
ok to start with they use 0.8mm steel, but you wont be able to get that. 1mm will be fine. the wheel arches are 1.2mm but you shouldnt need to replace any of that, just oxy and hammer out that RHS wheelarch dent. itll take time, but it can be done.
your best bet is to start drawing circles around the holes you wanna keep and crossing the holes you wanna weld up. smoothing properley will take AGGGES, so no need to rush. if you rush, youll be sorry later down the line. things to consider are:
1. the wiring. where is it gonna run, how are you gonna run it, how are you gonna secure it (VSB4 states all wiring needs to be secured at 600mm and protected against rubbing) zip ties are great, but they will require holes to feed through, so youll need to drill them before you paint so they are sealed. you gonna add any relays for horns, lights, thermo fans etc? where are they gonna be, how are they gonna run?
2. throttle cable, kickdown (if it needs it) fuel hose, carbon can, vapour hose, etc
3. wipers
4. overflow and wiper/washer bottles. if you are gonna change these, best source the new ones first, then fit/mount them properley, mark their location, then remove again ready for paint.
5. headlight wiring SO IMPORTANT. the uuuugliest bit of VK/H bays is the fact that fkn wiring is totally visible. re run all that ****.
thats all i can think of of the top of my head. good to remember also, on the base of the strut towers is seam sealer. DO NOT give in to temptation and remove this and replace with bog, unless you never wanna take a fast corner. bog will crack and lift. best bet is to take your time with a razor blade and smooth the glue as best as you can, or cover over it with sikaflex. you can get sikaflex nice and smooth using a sponge soaked in dishwashing liquid.
prepping for paint means running over the whole bay with a wire wheel, cover with deoxidine, sand it back with 120 grit, weld up the AC holes in the firewall, knock out any little dents, bog over most of the seams, bog over spotwelds. hi-fill, then more hi-fill, then more hi fill, wet sand with 400, pin hole filler any spots you missed (there WILL be places that need fixing) hi fill again, wet sand with 800 then paint.
the whole process should take around 40 hours. if you do it properley. but that doesnt include the drying time of the hi-fill. you really need to give it heaps of time to go-off, otherwise the heat of the engine bay may cause it to craze later on.
heres one we started earlier:
please note, sabbath rushed this one. there are spots we shouldve spent a lot more time on.