Cut-N-shut homemade frame, forks and bar/stem combo.
Chainstays shortened by 70mm, BMX droputs welded in, braze-ons removed. Bottom bracket 295mm from the ground
Forks shortened, straightened with v-brake bosses repositioned and disc caliper mount added
26" wheels - disc compatible - rear is 135mm axle with freehub and two gears(19t and 14t), generic MTB deep-V rims, 36 spokes, Schwalbe Marathon tyres
Linked V-brakes with option to use discs
GT/Profile three-piece cranks, Tree Splinedrive 25t chainring, Euro BMX bottom bracket, 1/8" chain. No toe overlap or pedal-strike even with 175mm cranks.
Only new parts are headset, bottom bracket and brake cables. Everything else is salvage, parts-bin stuff or home-made. Total cost, about £50 or so.