No you cant bolt in other b-series engines without major modification. The b20a5 was designed to slant torward the firewall to allow the hood to have such a low profile (lowest profile on the market). If you were to swap in another type of honda engine it would be the H22a because that's just what people have been doing. And it costs upwards of 7 grand!! That is a realistic here, i'm not inflating it to scare you. If your customer wants to swap in another motor, it should be the JDM b20a (ba4 prelude). Any other swap is territory for pioneers. If you want more information, go to
www.preludepower.com and search under "3rd gen" and type in whatever you want to search for (i.e.: engine swaps). Hope that helped (truth wise).