There should be an oil gallery plug screwed into bottom of right side crankcase. you can fit a pressure gauge there and see what pressure you really have.
The shop who told you 4~5 psi probably looked at " A "manual and only saw that's the switch pressure. In my opinion Honda did a real dumb thing and mounted oil pressure switch on outlet side of pump so oil light goes off as soon as engine starts to turn over. (and if oil light comes on when engine is running, it's already too late to do anything)That's why I said to check at main oil gallery. I would just get a spare gallery plug (or a short bolt that fits) and drill/tap for a banjo fitting, there isn't any need for a $300.00 gauge as a normal cheapy one will work fine (even if not 100% accurate)The gallery plug is a 'standard' Honda thread so picking on up from crashed/destroyed motor shouldn't be too difficult I did buy genuine Honda vacuum gauge set though - in 1978 it cost almost 3 weeks wages but still works fine today so guess the extra quality was worth it (the 'new' mechanical ones were no better than any aftermarket set )
this might do ithttps://shop.advanceautoparts.com/p/autometer-banjo-bolt-2276/10455285-p?c3ch=PLA&c3nid=10455285-P&iv_=__iv_p_1_a_810678608_g_40371513285_w_aud-296857279645:pla-329229809404_h_9009610_ii__d_c_v__n_g_x_pla_y_6201684_f_online_o_10455285-P_z_US_i_en_j_329229809404_s__vi__&utm_source=ACQ&utm_medium=cpc&utm_campaign=PLA&utm_content=shoppingcampaigns&gclid=COn-ja3nndQCFdY9gQod7OgDbw#fragment-4http://www.autozone.com/fittings-and-hose-line-connectors/fuel-fitting/russell-m12-x-1-25-banjo-bolt-adapter-fitting-with-1-8-in-npt-female-port-for-use-with-russell-640910-641110-and-641120/773861_0_0
I think the pressure switch is a 1/8" BSP taper thread?You should be able to rig something up for less than $50.00. Probably not a good idea to have it permanently fitted, the pressure variations can be frightening (even though it's normal running condition)I just had to dig out manual as I've been confusing myself with the oil passages. Isn't it possible to remove the gallery plug on top right side then fit a banjo bolt there? (similar to SOHC placement although 'hidden' behind alternator cover)If you replaced the line with an Aeroquip (or similar) stainless one you could have that Summit gauge permanently mounted.For $25.00, can't go wrong