One unon fund (call it Widget Workers) wants to make a loan to another fund (call it Widget apprenticeship) for purposes of purchasing land to build new building for training. Funds have some, but not all, common trustees....ignoring the issue of this being a prudent investment, is this a PT? Anyone aware of similar situations with PTEs obtained?

This would be a PT. As to the common trustees this would be a violation of 406(b)(2). However there are a number of DOL advisory opinion letters that can help you structure this transaction to avoid problems. In addition that are several class exemptions that could come into play. Start with PTE 76-1. Since this involves real estate, you probably want to have a QPAM involved, otherwise your fiduciary liability insurance may not provide coverage.