180 is NO way stock, surely? One of my chums has a Renaunt 19 motor in a 440, and with a 2.0 stroker crank, programmable EMS, etc, he's pimping about 150bhp (estimated at the fly, measured at wheels). A turbo kit is available, but the engine is too weak to take much boost on stock internals, so it's not really worth the £1500 or so it costs! If you want to start pushing the boundaries in terms of power, prepare to shell out for a forged bottom end...and that costs serious £££. Still, a very nice project...you'll have me in the corners, but I'll get you on the straights. Having said that of course, your project will actually happen sometime this century...
Ironically you picked the two lighter motors there when you said the PRV and T5 motors are too heavy. The T5 whiteblock motor is actually pretty light - I don't have the specs to hand, but I'd be surprised if it's not lighter than the stock redblock in the 360. Likewise with the PRV - all alloy, so it weighs almost exactly the same as a redblock turbo, despite being huge! Of course there are those who argue that the redblock is too heavy for a 360....and I'd not necessarily disagree, although I'd like to think we all know why it happened that way.
What may not have come across in my description is that 'phase two' of Nessy - the spaceframe chassis - will turn her into a racecar. This is a seriously long-term project, and is even less likely to get off the ground than the 'monster engine' phase, but done well it would undoubtably be the best handling '300' on the planet - simply because it wouldn't be a 300 at all - rather a racing car clad with 300 series panels.
Dropping an uber-light all-alloy motor (how about a B4204 x40 T4 motor? May well be lighter than any original 300 series engines) into a 340 chassis is a tempting idea I'll admit, but there are limits to where it will take you, especially given the relatively heavy weight & poor aerodynamics of the shell, plus the relatively narrow track. There's no denying that the transaxle layout makes for a great rallying chassis, and every project - no matter which path you choose - adds to the rich diversity such a flexible platform facilitates.
I'd currently looking into a lowering and stiffening package BTW - do let us know more about the route you're taking. What shocks have you gone for? When you say you replaced the anti-roll bar...with a new replacement, or a thicker one?
cheers
James