Gary.
I think Basil should have a section on this board for modifieds, as not only V8's but V6's, Rotary's , Toyota's and even turbo's are going into MGB's. This is because people love to do their own thing and create a one of a kind that is "theirs".
Their are 2 ways to build a faster car, one is by using a bigger engine, the second is to build a lighter car. It has been said that engine size was the start of the demise of Detroit, because they kept building bigger and heavier engines, which of course made for "yank tanks" while the rest of the world worked on smaller lighter more sophisticated engines.That is why the Rover 4.0 ltr engine is so good, it actually started life as a Buick 215 but was rejected by GM and replaced by a larger cast iron motor. It is all aluminum, heads and block and is 40lbs lighter that the cast iron 4 pot MG lump. Replace the 8.13 to1 pistons with 9.75 pistons, change the cam, a little head work plus a few other changes and you have a 2000lb car with close to 200bhp.
Once you have driven a MG with a V8 you will want one. If we ever meet up at a show you can drive the Silver Lady and see what I mean.
Regards