Hi peeps. I found a bloke on Facebook that does resin engines and wheel wells for the Minicraft 737-300. Apparently the wheel well will even fit the Airfix -200 with slight modification. I've been talking to him on FB and will be ordering a set of engines and 1 wheel well so I'll let you know what they're like when they turn up. Here's a couple of listings of them on eBay. He has said that ordering from him direct will get a discount.
Engines
https://www.ebay.com/itm/283066495146?ssPageName=STRK%3AMESELX%3AIT&_trksid=p3984.m1558.l2649
Wheel well
https://www.ebay.com/itm/283052986884?ssPageName=STRK%3AMESELX%3AIT&_trksid=p3984.m1558.l2649