Trevor,

First, if I may ask, are you located outside of the US? I have never seen a 240GLE of that vintage in the 'states.

To address your question, to the best of my knowledge, it is possible to put a DOHC 16v B234F head on a B230F block, however this engine has some reliability issues. The B234F is an interference engine, meaning that if the timing belt breaks the pistons and valves can be damaged. If the timing belt breaks on your B230F, all you do is install a new T-belt for about $20 US and you're back on the road again in less than a half hour. While the "seat-of-your pants" sensation that the 16v engine can produce is fun, I find the B230F's combination of power and economy to be more than adequate with a 5spd gearbox (is your GLE auto or stick?).

If you really want some extra "oomph", IPD (see link below) sells a 'VX' camshaft upgrade for US $189. According to their catalog, it is good for about 12hp over stock and takes up to 1.2 seconds off your 0-60 time for a non-turbo motor. That might not sound like much, but it's more than a 10% increase in power. This would probably be less expensive in the long run than swapping heads, and produce similar results. You might also consider upgrading to a hi-flow exhaust (good for another 5-6hp). :-)

Good luck with your "new" 240!