I have an early '67 Swedish domestic market B18A in my Amazon to which I have fitted a D cam, B18B spec head, twin SUs and a four branch manifold & Simons exhaust. The engine has 230,000 km on it (144,000 miles), runs well, has plenty of power, does not burn oil or produce any visible smoke and has compression readings that are even and well within spec. When I swapped the head, I noticed that the bores were smooth but had no wear lip. I know that it would have been a better idea to measure the bores for wear and at least have them honed at that point before matching a higher compression head to old rings but I didn't and here I am.

The engine has the old style breather setup where the crankcase is vented through a steel gauze at the side of the block and then down a small pipe that vents to the atmosphere near the sump. There is no recycling of gasses for emissions purposes.

The problem I have is that there is an exhaust pulse from that pipe and the gasses from it are entering the cabin. This has been an issue since I fitted the new parts. At first, I assumed that there was a broken ring on one cylinder or just general wear and that this was causing blowback. It struck me recently that the B18B always had exhaust gas recirculation and that the pulse from the crankcase vent pipe on my engine might be just because of higher crankcase pressure created by the higher compression head. That said, exhaust gasses shouldn't be escaping past the rings into the crankcase should they?

Anyway, I have no means of doing a leakdown test so the only way that I can truely verify the condition of the rings is to strip the engine. Before I do that, I thought that it might be a good idea to ask for other perspectives.

Do you think that the issue with my engine is likely to be rings/bore wear and that I should tear down the block or if I need to consider fitting the later breather system?
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1967 131, 1977 Volvo 245 DL, 65 VW Bug, 71 VW Westy