That screaming good deal might cause you a few screaming nights of frustration. As Blaplante mentions the lower cowling will most likely need to be modified with a bump so that it clears the alternator, regardless which one you use. Even with the standard Vans 40A alternator it still requires additional clearance.
Blaplante is also correct when he states you will need to modify the engine mount top brace in order to fit the engine into the mount - which will require you to cut that top tube out and weld in a new piece.
The stock Vans Baffle Kit will not fit the H2AD and you'll need to modify most parts.
You will need to cut the top engine cowling and place bumps on top to clear the two bosses at the frount where the fuel pump bolts on (front left) as the engine hits the cowling at this point.
You will not be able to leave the engine lifting eyes on the engine when fitting the cowling. No great drama there, but whenever you need to remove the engine for some reason you will need to remember where you left those lifting eyes so you can reinstall them. You might laugh - but in 15 years time I bet you won't remember where you left them.
The cut-out for the oil dipstick is higher up on the top cowling than the location provided for on the standard Vans epoxy cowling. Again, not the end of the world... but more work.
Once you commit to the H2AD you will pretty much need to stay with the H2AD as the cost to change everything over in the future to a different engine model is prohibitive. What I mean by this is that you can (reasonably) easily change between most models of engines without major changes to your firewall forward setup, but the H2AD is different in almost every aspect. All your fuel and oil hoses are different lengths too so you can't buy Vans's firewall forward kit and expect anything to fit.
All of that said, the H2AD is an honest 160 HP engine and as long as you look after it you should be right. Be sure to check that camshaft though - after 2,000 hours its likely to need replacement. The good part here is you can take remove the pushrods and followers from the engine without pulling the cylinders off and inspect the cam lobes.
Good luck with the installation.
Cheers,