Gents, thanks for your input & ideas. I agree a hard line approach would be optimal from safety standpoint but at least for now I opted for a basic solution that will get the cooling system back on line soonest.
Steve, funny you mention the lack of a retaining rib on the heater core...I never had that exact problem, but the ribs on my steel tubes coming from the chassis WERE compromised by corrosion and were useless. Bottom line I ended up trimming the tubes back several inches, positioning the sealing clamps in the front trunk area, vice under/behind the heater (see image; this approach cut the number of hose joints in half, compared to the previous solution). Since the ribs were gone anyway, concern for originality wasn't an overwhelming factor. I went with silicone hose sections made in the UK for a Morris Minor - 1/2" ID vice the optional 12mm but should work fine.