V-8 swap questions

[mecwpri]

Been lurking in the 60-66 forum for a while as that project needed attention. I plan on swapping the 4.3 out of my 4 door blazer, 1991 vintage for the 5.7 out of a wrecked 89 or 90 van that I have. I plan to freshen the v-8 prior to install, my question is motor mounts, will the factory 4.3 work? seems everybody wants to sell 2.8 mounts and adapters, seems like a week setup to me. Also plan to use factory exhaust manifolds and remember reading somewhere that firebird are the desired ones? any help here? Will the ECM need work or will the van ECM work? how about the factory 4.3, will it work or what? I would like to keep all the factory accessories and factory look, dont want any bling, just more power.