why not save money until you can afford a faster car and insurance for it!
modifying a car and not declaring it, is breaking the law, and also declaring modifications means you may have to spend from 1/3 to 1/4 more on your insurance! and major modifications like an engine swap can make insurance more expensive than just insuring the car that the engine came from! as well as any labour costs to fit the engine!
Unfortunately, as much as I hate myself for saying this, since I was previously a D series fan. The simplest and easiest way forward is to go B series. I pissed about a lot with my D16. I'm sorry clinchy, but you'll see the light one day my friend.
Tempting but not planning to spend that much money on it really.
Plan is to get the EG shell that I have seen and then get a writen off MB6 or an aerodeck and then use all the stuff that I need from there to build the EG. Will then throw that onto LPG, sell the BMW and use it as a daily driver. Thats the plan anyway, just so long as everything happens as I'm hoping it will.
Don't know really, depends on the engine. I guess you could say if you have a full system, including manifold, highflow/decat, and the cat back of the system, you might free up 5-10bhp (probably get you back up to stock power!), but you could probably gain that by merely having it dyno'd at two different places since the readings can be so far out lol