I haven’t managed a close look either! Walsworth Models do a very reasonable 7mm kit - etched nickel silver and motor, wheels etc included - for just under £110. For an extra £35 or so he’ll even build it! Might be a good way to start in 36.75mm. Easier than doing a single wheeler -only a fool would start that way! https://www.walsworthmodelservices.co.uk/product-page/sentinel-y1-3
I think the NCC Sentinel had double windows but a bit of work with a piercing saw could sort that. And if it all goes badly wrong, just build yourself an SLNC railbus trailer with the chassis!