Excellent budgetary optimism
Neither of the budgets would work. £10k is a non starter. £30k...with you doing all the work, every last bit, just might get a what you're after. And the only engine worth installing would be a proper V8, a Dodge Viper V10 at a push. A soon as this happens costs go skyward as the whole driveline gets into serious mode...and then there's suspension and brakes. But, how would you get insurance on a heavily modified vehicle even with theoretical IVA? Re' budgets, ask me how I know - I've built many classic cars and am currently refurb'ing my D90 SoftTop - I won't tell you how much the final cost will be...read a lot...with me doing all the work except for the engine...which Turner Engineering have completed supplying me a brand new block, all new internals, modified head...+++
new copper radiator
AliSport IC
Gwyn Lewis HD steering components all round
Terrafirma dampers
OMU steering
Diesel Bob Bosch VE pump
new brakes all round
new brake lines
new master + slave cylinders
upgraded clutch components
new master + slave cylinders
new bushes all round
full refurb & chassis repaint in bedliner
rebuilt TurboDynamics turbo
new exhaust
redesigned and rebuilt heater
new YRM footwells, inner sill rails +++ all new st/st fixings and fasteners throughout
Dixon Tree/Rock Sliders
refurb'd front and rear trailing arms
refurb'd A frame
new front electrics
new Alternator
new front light
Mazda RX8 seats
Leather Chubby Box
refurb'd bonnet with Dynamat
cockpit and door soundproofing
Raptor Dashboard
new gauges
original Wolf Wheels
a whole host of consumables + smaller parts...the list goes on and on...
The objective to the above is a a superb condition underside, running gear and underhood/engine bay...with a 'nicely used' but clean bodywork. Admittedly the old girl will be mechanically perfect and super strong when finished but all these things cost money [and don't ask how much I spent on the MGB V8 Sebring Roadster, again with me completing all the design, component specification, bodywork and full mechanical build...this would have cost £60-65k if completed by a Fisher Services type Co]
Good luck with whatever option you choose...and if I can offer one word of guidance...complete a thorough project.xls budget before you start, then at 15-20%...then have a stiff whisky